I don't know for 100% certainty, however I would think that the electronics in the headlight are designed to run at a certain current draw and the heat sinks are designed around this. If you are doubling the output, you're also substantially increasing the head that is generated by driving all of the LEDs at the same time, I doubt it was designed to do this. My understanding is that it's not designed like your basic plug-in LED turn signal or tail light. The light output is substantially higher.
It's also a pretty expensive headlight to be attempting to modify. Just my 2 cents.
The easiest way would be to run a big diode from the high beam +12 to the low beam +12 so that the anode is pointed to the high beam.
When the low beam is on, the diode won't conduct. When the high beam is on, the diode will conduct over to the low beam.
The downside to this is the diode will exact a "toll" and .6V will be dropped on the way over to the low beam. You might not notice it.
A better solution would be to use a relay. Personally, I would add a relay and then have the relay turn on a pair of sweet driving lights and leave the low beam off. (That's what I did and I love it.) Here are some lovely relays: http://www.easternbeaver.com/Main/Elec__Products/R elays/relays.html The one I am using is the 20A micro with tab. I carefully shaved a bit of insulation from my hi beam wire and soldered a wire to the copper and it's been there for about 30,000 miles.
Here is where you learn from my mistakes: #1) Reinforce the ground between the steering area and the front of the frame. #2) Run a fat wire directly from the battery + #3) Do not use a fancy thermal resetting fuse breaker thing. The heat under the seat will trip it! Use a plain old fashioned fuse.
Before you go thinking you need MORE light think about making sure the lights are adjusted properly. Mine and several others had the light adjusted way too low from the factory. A few turns of the adjustment screw brought it up to spec and it put out a ton of light: A)Without blinding other drivers, B)A pure white light that really lights up the road and reflects off everything well and C)has a shape that focuses the light not just out front but also well off to the sides.
The HI Beam is also amazing at night but when adjusted properly its too bright for other drivers and I find it has a much LONNNNGGERR throw than on would expect.