From a google search:

there is a hole on each side of the wiper
compartment that lets you get a screwdriver in the latch mechanism.
give it  a twist and it will release. then you can fix the prob. its
under the hood a  little and you will have to go by feel. but you
should be able to see the hole with a droplite, then go from there.
used to have a url for a pic of
how to do it , cant find it. do a search on the corvette forum and its
there
someplace. good luck, regards, j.d.

And from Mid America's website (with some pics):
http://www.madvet.com/shop?frame=4.264.3852

Let me know if you need me to copy the article here if you are unable
to browse the web.

--
SkyhawkXP
Seize the pleasures of the moment,
without concern for the future

========================

Lots of luck...   This has happened to all of my C3's at least once
over the years.
Since it is the passengers side that will not unlatch you may luck out
and be able to reach under the near the drivers side of the hood and
find & pull the cable ...this works if the cable is still attached on
the passengers side ...

If that is not the case I have found that it is not all that difficult
to get on the ground and using a long screwdriver reach up and get to
the latch and push the lever towards the center of the car...removing
the lower splash shield from the rear of the fender area  makes
getting to the latch prettty easy...just 3 screws if I remember
correctly...

Frustrating  job...what can I say......

PS.... I read about the access hole in the wiper area BUT I just
walked out to the garage and looked at my 76 (the hood was already up)
and I never found any hole...