If you have a counterweight available, you can connect the straps to it and belay the straps. That way, as it slides down you aren't dealing with the wieght, just making sure it stays on track. A window opposite the stairs would allow you to tie it to a car, a tree, or similar. Looping it around a tree would create a pully. The ideal equipment would be a repelling type harness. I have seen a simiar method used to lower a cast iron furnace down some stairs.