dusty wroteI know several turners who have elevated their Mark Vs for this very reason. It seems to work but I just have to worry - with the center of gravity elevated it becomes more of a tipping hazard. If you elevate it very high, I would think you'd want to secure it somehow or elevate it onto a fairly large surface area (something significantly larger than the legs' footprint).
You could always fasten a 4"x4" post (about 3 feet long) under each end of the legs. If that's not high enough, you could fasten a couple of rail road ties to the bottom of the legs. Just don''t think you would have to worry about tipping in either case. If the ties are too high, you could mortise out a portion for the legs.
Nick once talked about putting a sand box under each leg (but I could'nt find the post) and burying the legs in sand as a means of stabilizing the lathe. Depending on the height of the box floor and depth of sand this could also be used to raise the lathe.
All in all, I'm glad that at 5'7" I don't have a height issue at all. (at least with the Mark V)