No tuners with RB experience in Sweden but I don't see what could be so hard about adding/subtracting the right amount of fuel at a given RPM and TP. Of cource it'll take more time since the tuner isn't used to the RB software.
Cam config or power has nothing to do with what fits. The injectors and engine management system SHOULD be the same on the HP2 as on the hexheads.
I'm sure I've seen a HP2 special with RB3 somewhere and there is
http://www.rapidbikeusa.com/uncategorized/rapid-bike-bmw-hp2-sport-performance-header-collector-kit/