The high voltage wire can be soldered off from the ballast side, but its one heck of a tideous maticouls job.
Drilling holes in rear of headlight is a better option. Many OEM ballasts (Audi A6 Healla at least) has a 2inches squared piece preassembled onto high voltage wire. This square should be relatively easy to retro into your own headlamp:
You probably alreasy have ballasts, so its probabaly not an option....