I guess I was lucky in that the footbeds appear to be a perfect fit into the boot liner.
How about a slightly different appraoch ? Try some ‘Off the shelf’ insoles from Go Outdoors / Sports Direct .
SofSole or Supafeet do various different ones. Will be better than the std one the boots come with , but not as good as a custom.
I think I am right in saying you are an advanced boarder , who has skied for a few weeks? Maybe full commitment to decent boots and liners is a jump too far. Decent boots with a thermo fit liner will still be comfortable from the second day you use them, just maybe not as comfortable after 6hrs skiing and an extended walk up a steep pitch to reach pastures new .
Snowheads might give the answer you are looking for ,Colin posts on there as well. Lots of informed people who know more about skiing than I do.
TBH its news to me that my custom insoles aren’t transportable between boots, but I can see the mechanics of each boot being slightly different , but there is alot of paddding in a liner which simply has to negate some of those differences