You say that converting Studiolith wheels for split frames is difficult but are you aware of Barry Luck's article in MRJ 19 ? His method is to use a 1/8 reamer in the wheel socket hole until a i/8 axle will go in half way. The axle can then be pushed the rest of the way in and is a firm fit in the wheel. I have not used this method with Studiolith wheels but have done so with the Alan Gibson brass centred ones and found it works well.
Barry's MRJ articles were, for me, seminal; I have never used any other method since. And yes, I have successfully used the reamer trick.
Rather than cutting the axle in half and then trying to cobble it back together straight and true I like to bore it out, epoxy in an HSS core (broken drill) and then cut the gap(s) with a piercing saw. This way the axle remains straight and you don't need any jigs (though you do need a lathe)
The trouble with the Studiolith axles is that they seem to be made of very hard steel indeed as they consumed quite a few drill bits before I was able to get sufficient depth for the core. Once they are done though they are completely trouble free.