yeah man you can do exactly that. i can sell you a d2s ballast with universal connectors on one end. the key is to piggyback the ballast off the headlight leads that go to the OEM ballast. Saves 100$'s over oem.
you'll need to poke around a bit with the ballast to get the right wires.
I run a canadian led kit & hid kit company, if you have any questions about led headlights or hid kits in canada or would like to check out our products please contact me here: http://absolutehid.ca
Hot: 2001 Estoril M RoadsterZCP 19's michelin supersports, ZHP knob, JL 8W3
Cold: 2002 TiAg M3 6mt
deoranged, dechromed, led tails, ZHP knob, UUC SS v3, GROM, OEM 18's w310's,
Fun: 2006 YZF-R6, black, ohlins, pazzo, cat delete, vance hines csone, YEC racing tune