Here is a concept for a simple vent-window prop, if you don't
mind the regular fumbling to set and remove it.

Glue a piece of coathanger wire between two pop-sickle
sticks.  The end of the wire should protrude a few
inches out from one end of the sticks, which themselves
are cut down to maybe 1-1/2" long.  Once the glue sets
up bend the wire back to form sort of a u-shape.  NOTE!
The orientation is important!  You will do it right if you
lay the sticks flat on a table and bend the wire UP toward
the sky.

Now glue-and-clamp a small piece of something onto
the bottom corner of the window (which is furthest
from the door when open).  I used wood with a small
notch carved in.  However you do it, position the
something-to-be-glued WITH THE WINDOW CLOSED
and don't get too snug against the frame so it will open
smoothly.

You use this contraption to prop the window.  Setting the
prop is simply a matter of opening the window, laying
the wire against holding-piece (whatever it is) glued
on the glass, and then anchoring the sticks against the
window frame with one of those 1-inch binder clips
available from office supply stores.  5 seconds, tops.

Not the solution for the aesthetic connisseur (sp?), but
a lot less monkey business than trying to get at the
tightening screws inside the door.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Steve