The only supported way to do that would be writing an XML description for the custom organ design module (CODM) and altering the stop-rank table entries for the mixtures. That is a lot of work. There are examples shipped with HW that you can edit (extensively) to try it, but I wouldn't do that much work for such a small gain.
Some samplesets don't support CODM at all -- don't know about Friesach.