One is to make the power valves " boost refrenced " which really isnt a terribly difficult mod to do, I can PM you the mod info if interested. The other is to use 10.5 Power Valves.
The 10.5 PV deal I heard from a guy who has been playing with Roots type blowers since the early 60's and has been using this method for over 30 yrs. I have never tried it, but in theory it should work fine.