Proper HID retrofits (replacing the whole projector assembly along bulb capsule and igniter/ballast) is a lot of work and $$$, but can be done. Check out the The Retrofit Source online: headlight upgrades for all applications if you choose to do an HID retrofit.
Checkout this guys legitimate RetroFit to see how it's done correctly: '13 WRX Quad Projector Retrofit
If you're keen on getting HID "White" look for "cheap" and easy then get yourself a pair of "Sylvania SilverStars H11's". If you want lighting nirvana for cheap and easy refer back to everyone's recommendation regarding H11 to H9 conversion.