I would imagine that slippage between the shims would be your biggest worry. You should be able to find the right spacers with some careful searching. Found quite a few options on ebay and aliexpress. Problem Solvers make them too although SJS don't seem to have them listed.
Hmm yeah slippage is my worry, but with one set of shims there's no slippage so I don't know if I'm over thinking it, but also don't want to end in fiery death...
Do you mean using 22.2->25.4 and then 25.4->31.8?
I would imagine that slippage between the shims would be your biggest worry. You should be able to find the right spacers with some careful searching. Found quite a few options on ebay and aliexpress. Problem Solvers make them too although SJS don't seem to have them listed.