This forum has given me so much, so here's my chance to finally help someone else...
My solution is to use Changescreen app. Link:
http://forum.xda-developers.com/showthread.php?t=466858
Changescreen has an option that turns off the screen when the phone is held upside down. It also allows rotation (landscape) in every screen, but if you don't want that you can turn off the landscape function in the properties. When I want to turn off my screen I just put my phone in my pocket upside down! Check it out, it works great for me!