Easy-peasy: just roll up a murderer and murder everyone you used to know. There are IG solutions here, guys!
But more seriously, I've also had this thought -- it only applies to city-based characters, since the Tribal/Luirs/Morins sphere is pretty isolated from the Allanak/Rinth/RSV sphere, so you can go: city, tribal, city, tribal, pretty easily. However, I do like having a lot of density in Allanak -- it in fact allows certain subscenes in Allanak to flourish (and as a result, you might not encounter them, e.g., gemmed and rinthers -- if there are a lot of gemmed and rinthers, you might not see very many gemmed and rinthers as a Borsail or a Fale).
So, on a whole, I think I'm happy the way it is since I can't see a solution other than opening Tuluk back up.