Remote desktop defeating inactivity timeout
I suspect there are ways in software to do this but I found a really simple solution by accident years ago. Assuming your mouse is optical, placing it on a refractive surface such as a frosted glass coaster causes the mouse sensor to move the mouse by a few pixels at a time almost continuously.
I use this trick every day as I operate a remote recovery service and some portions of the service can lag for hours, I use this to keep the session active while I move onto other projects. I picked up a set of the coaster, 4 I think, for about ten bucks last time I added workstations and find it a simple technique. One warning though, if your mouse is wireless this will cause you to run through a lot of batteries so use rechargables.
I found this question searching on Google and one possible solution is to have a program that automatically moves your mouse every X seconds and does something (like click or press a key). Here are a couple of free solutions I found:
http://movemouse.codeplex.com/
http://www.murgee.com/auto-mouse-mover/