Ziggy, you can first by using the shortest manifold you can find. Go with a pipe that would also give you the shortest pipe combo. Shorter pipe length will give you better top end at the expense of some bottom end. But then again, the bottom end of the FW05R is already very good...

Also like some already suggested, add one more copper shim to increase the combustion chamber height. It works for me and the engine revs much more easy at the top end.

If you still cannot get the engine to rev high, then the only option is to gear as low as possible (using Kawahara 0.8 crown gears) to get as low FDR as you can to shift the gearing to accomodate and take advantage of the engine powerband.