Thanks everyone for all the advice! To sum up there seems to be no easy solution. I only have the option to either - make things really complicated - only help some users/query structures - accept the status quo
What could help is an analogon to field aliases: If it was possible to say f.title.pf=title_exact^10 title_proper^5 analogous to (the existing) f.title.qf=title_proper^10 title_related everything should work just fine But I guess this will only come if or when one of the developers has an itch to scratch ;-) Anyway, thanks a lot for all help and a great product --Michael