The leg threads are 3/4"-10. (ten threads per inch)
You can go to the Homely Depot and get two-foot-long 3/4-10 threaded rod, threaded couplers, nuts, and a 3-inch bolts. If you use the coupler to attach the bolt to the bottom of the threaded rod, you will have a 27-inch leg.
I used a nut at the top of the leg as a stop (to keep the leg from screwing all the way up through the bottom of the piano).
The parts aren't cheap, so it will cost $50.00 for four legs.
You will NOT love the results very much. The legs are much too heavy to gig with, and they feel sharp an annoying to handle. However, if you just leave the Rhodes in one place like I do, these legs work great.
Oops! I have already posted this recipe:
http://ep-forum.com/smf/index.php?topic=6226.msg30513#msg30513