Crap 2GTEU has my book, maybe he can pipe in. It has been done on a OEM car in Europe back in the day, forgot why as in what sports it pertained to, I think possibly for WRC, and I can't remember the company but I'm sure 2GTEU will pipe in.
Only reason to do it would be to have a roots type supercharger and a huge laggy turbo, but that was then, what I mean was the car was made a long time ago, when turbos spooled up slower than all hell back in those days, but had awesome top end benifits that we all know of, so they made the freak car to have both low end of a supercharger and the high end of the turbo.
With the spool rate of turbos now, I would assume people would do it now more for show and cred than to make it really make a difference at the track.
B.
*EDIT* thanks G0ddang for the post with pics, notice that its a roots type supercharger, a cintrifical would defeat the purpose. Also props the the STi guy, being factory boosted it might have costed much less than it would a NA to boosted car, and also I hear with the mani's that the Subis comes with, he could probably use the low end boost, those cars lag like a fat boy in PT class.