Jerry's idea works perfectly well, if you've got an extra transmitter that you aren't using, or can get one cheap. Most of the one's I've seen for my opener are around $30 or so.
As stated in the other thread I started, the Flash2Pass is VERY simple, inexpensive ($58.95 on Ebay), and in the long run, a better solution if you still want to use your high/low switch to open/close the GD. There are other ways to make a standard GDO transmitter work off your High/Low beam switch, but they are more trouble than the Flash2Pass. You tap into two wires (white and black), and they provide two decent wire taps to do so, so you don't have to do any soldering if you don't want to. Yes, it's better to solder the wires, and I could have done so, but I chose to use the wire taps just because I did not want to cut the wires. There is only one potential issue with the Flash2Pass...the receiver, in some cases, has to have an external AC power source, but if you have an old cordeless phone charger laying around, that will work, or they sell one. It's a common thing though, and Radio Shack I'm sure has one. But that depends on what kind of opener you have on your garage door, and you won't know 'till you hook it up and the LED doesn't flash. I have Genie (old ones) openers, and I had to hook up an AC source, but had a charger laying around that worked perfectly.
So, you can do the HID's like I did, with the slim ballast kit for $149 (there are others out there too), get the Flash2Pass, for a total of around $210, pull the fairing off, hook everything up, test it, and you're good to go.
Or, you can wait on a LED solution for around $700 and still not know for certain the HD GDO will work with the LED's.
Believe me, I wanted the HD GDO to work just because I already had it, and a person who wanted to take the time to build a relay to make it work could do so, but at some point the thing is more trouble than it's worth. Having the MUCH, MUCH better light on the front of the bike is worth it.