I did something very similar to my r and wish I wasn't TDY right now and I'd come over (or vice versa) and help you out first hand. But since I can't here goes.
First off - what have you done with the high-beam flasher so far?
The circuit that kajer came up with uses the flasher button as a relay to supply power to the relay. You need to find the "switched wire" coming from the highbeam flash button in the harness and use it. It'a bit hard to find, but I found it inside the black sheath. Also, there are two places that the wire goes to, if I remember correctly - I'm not 100% sure of where they go again. You'll have to check the wiring diagram for that one.
You then wire the switched portion of the flasher button to the coil of the relay along with a ground wire. When you hit the flash button, you should now hear the relay click. Next, take the low beam wire power wire (from the battery) and connect it to both commons. Connect one of the normally open outputs to the ballast and connect the other output back to the coil where the flasher button wire is connected to (make sure you don't accidentally connect it to the ground wire!).
This *should* create a circuit that does the following:
1) push the flasher button
2) the coil energizes
3) the commons get connected to the normally open terminals supplying battery power to the normally open contacts
4) the HID ballast receives power from one of the normally open contacts
5) the coil stays energized from the power coming from the other normally open contact.
Hope that helps.
Ben K.