Two things though that I am sure you thought of -- you are going to have to see the control panel to get the treadmill to start, and putting a desk on the handrails cuts the actual treadmill underneath in half (at least thats what it looks like from that picture), which can be kind of dangerous - you need enough space to actually walk (you don't want to be concentrating on carefully shuffling and not falling off, you actually want to concentrate on work, lol).
Are you wanting to put your computer and everything up there like the photo? I was just curious
(And I'm curious to see how this project will turn out, its a cool idea!).
In the meantime... are you using the treadmill?