Well, opening up the wastegate hole in the turbine cover and adding a matching ported elbow with a larger puck isn't a bad idea...
You might try one other thing first. Do you know how to hook up the wastegate "tuner style"? Well, here you go:
Remove the stock boost line (the black vacuum tubing with plastic elbow and Y fittings) from the brass fitting on the compressor cover and the nipple on the wastegate actuator.
Leave the boost line connected to the wastegate solenoid, and leave the solenoid plugged in. Just tie the boost line up out of the way for now.
Run a new piece of good quality vacuum tubing (I think it's 7/32", you'll need maybe a foot of it, from Pep Boys, for example) from the fitting on the compressor cover directly to the wastegate actuator. Put zip ties on both ends so it doesn't come loose (kaboom).
See if this helps...