The only real benefit to the MAF relocation on the MSP is that you can locate it after the BOV and run full VTA without all the stalling/rich condition crap. Boost creep is typically more indicative of having an exhaust setup with too little backpressure, such that the wastegate cannot dump enough exhaust at higher rpms, and you keep building boost even with the wastegate wide open. At that point an external wastegate is what you want.
Aside from that, there's the practical issue of whether or not a given MAF can function correctly as a blow-through sensor. I'd be very concerned about whether the MS3's MAF is capable of holding up to 18psi without leaking or even blowing right out of its port.
EDIT: Just noticed you're from the twin cities area... you should pop over to mnmazda.com when you get the chance!