the trunk?

Here's a dumb question.  I have a '98 Intrigue, it came with two remotes,
two black-topped keys, and one regular metal key.  When they sold it to me
(used), I was told that the black-topped keys were the masters and open and
close everything and start the engine, but the metal one would only start
the engine(and maybe open the doors - I don't remember if they specifically
said so).  The point of all this is that you can put your valuables into
the trunk and give the valet only the metal key so he can't get into the
trunk or the glove compartment.

Now, here's the problem.  All three keys open and close every door and
start the engine, and I can't find any way of overriding the trunk open
button on the dashboard.

I can't find anywhere inthe manual that talks about this, and no one at the
dealership(Oldsmobile, if you can believe it) knows how to do this.  If
anyone has any insight, I'd love the hear it.

Thank you in advance.