[saurik]

Which is why PostgreSQL is scriptable: the various contrib modules are often better looked at as examples of how to build your own indexes using GIN/GiST than "this is what we provide".

In your case, though, a strict immutable function mapping the bitvector to an int array as part of a functional index should be sufficient to use the existing contrib module: you don't need to store the things you index in the table.