FYI - here's another solenoid you can use. Its very similar to the perrin but w/o the daft markup its 55 yankee dollar*.
store And this direct link might work...
product link worky? All these one's should be close to plug and play with the Pierburg (they will flow differently but duty cycles is pretty universal).
However, can't help but think that the boost take off in the intake is not the best place - nearer the compressor wheel would give it better control, no?
ps) * Mr Dom is a nice chap and postage is cheap (but rather slow)