Show some data on your EMP's vs IMP's before you can determine if that's going to help.
Do you have boost creep at higher RPM's, is your VNT actuator vacuum going to 0 during this period?
I've played with an external wastegate in parallel with a VNT and unless you have boost creep with zero VNT actuator vacuum (assuming your actuator is setup properly), an external wastegate won't help. EMP's will be limited, however boost will fall with it, MAF falls and power goes down and/or smoke increases.