I am an equal addict to coffee while driving. And driving the P-car is what I want. So a coffee cup holder is a requirement. I am immune to all the flames thrown by purest out there so here goes...
I built the most overengineered coffee cup holder you can imagine. It is shown (and I get flamed) nicely on Rennlist. Go to
http://forums.rennlist.com/ and search on cup holder. Look at cup holder for an '86.
Hope this helps. May not be much better than the "cup in the old sneaker" techique but my carpets are clean and I'm a safer driver when I'm not diving for an imminent spill.
Good luck!
CL