I am in the midst of building my treadmill/standing desk workspace now. I work at home, so have lots of leeway, but a few of the ideas I have come up with might be worth contemplating, if a bit expensive. I am trying to remove as many of the impediments to my using this as possible. Just standing all day or walking all day leads to pain and suffering, just as much as sitting all day does. The idea is to mix it up. The solution I have come with is to combine a treadmill desk with a standing chair, on a raised platform level with the treadmill.
I have a Lifespan TR1200DT treadmill (http://www.lifespanfitness.com/tr1200-dt3-under-desk-treadmill ), the 'best' option available right now...you can get two TR1200's for the price if you are thinking of getting the TR5000. There is a new brand of treadmills coming out from iMovR soon that will be designed from the ground up for under desk walking assuming the quality pans out.( http://www.imovr.com/imovr-the... )
I also have a Focal Locus leaning/standing seat chair as well.( http://www.focaluprightfurnitu... ) This will help relief some of the pressure from standing or walking all day, without the same downsides of sitting.
I am still working on a desk, though the iMovr ThermoDesk ( www.imovr.com/omega-everest-electric-sit-stand-walk-desk-with-embedded-ergo-tilt-keyboard-tray-48-tabletop.html ) is the one I am leaning towards. I am still figuring out the keyboard tray aspect given my personal preferences.
What ties it all together is a custom raised floor around the treadmill (2x4's, plywood and some nice hardwood looking vinyl flooring for a couple of hundred bucks). This allows me to easily wheel the Focal Locus on top of the treadmill or off to the side on the raised floor without lifting or strain, and quickly in seconds. The wheels of the Locus sit on the side rails, while the rear T which is rubber sits on the plenty sturdy enough treadmill belt. You could also have a semi-hard but light foam board cut to size to drop over the belt if you were worried about damage/wear.
Beyond that I am working on using 'light' voice recognition, additional mouse input options (handheld adesso easycat for when I am just browsing around...I'm disappointed with the wireless offerings being so large or requiring 2 finger scrolling) , x-keys buttons, etc. to help reduce the sheer volume of buttons and clicks I press each day, hopefully by 20-40%.
Hopefully someone else's lightbulb goes on from this idea.