With some good advice from John Davis and the help of a friend I think I've managed to come up with a workable solution.
My friend managed to track down a length of 11tpi threaded rod to fit the inserts on the guitar. He used that to make removable two-inch extension tubes that attach to the top of the front legs. Essentially the rod is set into threaded aluminium tube.
Then of course I needed longer pedal rods. I thought about trying to make new ones and might still do that in the long run, but in the meantime, here's a bodge that seems to work. The existing rods have an imperial threading but it's pretty close to M5, and will take a 25mm rod extender hex nut. So I used one of those to attach two-inch lengths of M5 studding. I had to buy new M5 ball joints as the original ones wouldn't mate with the M5 thread. They're a tight fit on the pedals but seem to work.
And after all that I now have a pedal steel that is two inches further off the ground and I can actually get my legs under it! All of the modifications simply unscrew if needs be.
Total cost has been around £40. I suspect that's a fair bit cheaper than having new legs made? Only thing that remains is to find some new rubber feet for the back legs.
