There isn't an ST specific how-to that I'm aware of. But the general procedure is the same regardless of what headlamps you're using, so with that said, a quick Google search for "HID retrofit project" or similar should turn up projects for other vehicles. The basic idea is you need to bake your headlamps to remove the front lens, cut out the rear of the free-form reflector housing so the projector can stick through, secure the projector to the housing, weather seal the back end, and install a shroud between the front projector lens and the rest of the stock lamp housing.
If you're good with tools and figuring things out, it should be a "simple" project, though be prepared for some fabrication.
