If your car has a seperate overflow tank and that is where you added
the oil, then I would remove the hose from it and drain it out.
Then flush with detergent.
Be aware that draining oil onto the ground may not be
environmentally friendly.

Well if your lucky just grab a turkey baster and see if you can draw the
oil off the coolant. Being you haven't ran it the oil should still be on
the surface.

Oil floats on water so since you have not started it up whatever you
put in should still be right on top.  Get some 50/50 antifreeze/water
and a turkey baster and inject the new anti freeze below the level of
the oil that's floating on top and force the oil to "overflow". Other
option is to open the drain and drain everything out but whether that
works depends on what kind of car you have and where the radiator cap
goes, etc, etc.

If I were to be the one to clean this up, I would unbolt the overflow
tank, then remove the hose and drain it into a bucket. Then I would take
the tank, now completely out of the car and clean it until I couldn't see
any remaining oil in it. Rinse it to remove any soap/detergent then put
it back in the car and fill with 50/50 mix.

Most overflow tanks I've seen are easy to remove, usually two easy to
access bolts or nuts,  but if your car has one that is inside the fender
or something that may be too troublesome. In that case it might be easier
to clean it in place.

The turkey baster (either sucking the oil off the top or forcing it to
overflow out the open cap) is a good solution, but how well it works
may depend on the shape of the tank in your car. On my car the tank is
wide and the cap is over on one side. I would be concerned that the oil
floating on the surface away from the cap would be inaccessible or
become trapped as to not flow out by adding coolant with such a tank.

Naw, that was just a little thoughtless. To make "idiot" you'd have
to, say, put power steering fluid in the brake master cylinder, as I
did ca. age 11 0r 12  because when Dad was giving me the chore of
keeping the leaky P/S system topped off, he was wrongly assuming that
I knew just where it was -- and had his hand on the master cylinder.
Then you did the right thing by not driving until you got an answer,
which was pretty smart.

First, did you put the stuff right into the radiator or into the
expansion tank?  The latter is what you do on most modern cars.  I'd
bet that little if any got sucked into the rest of the system.  If you
put it into the radiator (or if some got sucked into the radiator
after you added it to the reservoir)  and then didn't drive the car,
it still hasn't gone into the engine proper.

Second, how much -- a whole quart or just a little?

Third -- I'm not sure what exactly it would hurt in trivial amounts.
Large amounts might turn into mousse and cavitate the water pump or
something, but it's going through metal, same as the motor oil, and
maybe some plastics and rubbers that have to operate in an environment
where they can and do get oil on the outside of 'em.

Fourth:  was it synthetic or regular motor oil?  We  haven't had a
long, violent, inconclusive argument about the relative merits of the
two on this group in a long time, so I just  thought I'd throw that
out there.

"But seriously, folks":  How to remove it. You can probably get most
of it with a hand pump or turkey baster, as others have mentioned.
Oil floats on water.  That's why, after a tanker goes up on the rocks,
they clean oil off seals and seagulls, not crabs and oysters.  Since
you sensibly *didn't* run the engine, I'd bet most of it is stil at
the top of the reservoir and/or the radiator.  As others have
mentioned, the reservior is, on many cars, easy enough to remove and
dump and flush, after you have removed most of the oil.  (In other
cars it is well buried and/or integrated with the windshield squirter
reservoir.)

I don't think you have to be really agonizingly thorough about this
unless you also poured in the packet of  salad dressing mix and the
radiator is full of those little seeds.   Look in the radiator
(warning!  remove cap only when the thing is cool enough to touch
comfortably!)  from time to time for a few days just to check your
work.

If it's been a few to several years, though, you could also backflush
the system using the kit sold for that purpose, and refill it with new
coolant and distilled water.   Since you didn't mention whether the
car as a "honk if you passed p-chem" bumper sticker, I'll spare you
the explanation of why you mix antifreeze and water instead of using
straight antifreeze.   The chart on the back of the jug lets you
compare the virtues of various proportions to the expected severity of
winters where you live, and the owner's manual tells how much the
system holds.  A 50:50 mix solves the problem so well for so much of
the continental US that most people just go with that. )

One man's opinions, worth what you paid if your ISP is cheap,
--Joe

what about the guy who told his doctor that for all the good those
suppositories
did he might have well shoved the up his a.s