Not sure what year/model car you're coming from, but i have an 04 STi, and here it is:
Its quite simple.
Step 1: contact 6gunracing (.com)
Step 2: order a full kit to suit what your car needs (you can get 05 STi knuckles for the front in 5x114.3 that are machined to retain whatever stock strut you use, i.e. 02+ wrx struts)
Step 3: Install new front knuckles. Quite easy. (remove old, install ABS ring, install knuckle) Then install new 5x114.3 rear hubs in your old knuckles.
Done. Enjoy the wonders of a whole new world of wheel fitment.
Of course a cheaper way i suppose would be to have your existing (or a used cheap set) hubs redrilled in 5x114.3 pattern and then reinstall. But hey, might as well get all new bearings and such while you're at it right (first method)?