I believe it would be too difficult to fit two HID lamps in the same reflector. However, you could use one HID lamp and move it forwards and backwards (with a slight tilt) to change the focus points and create your two desired beam profiles. Most dual-filament headlamps have unique reflector profiles that has two different focal points. One reflector profile may focus or even diffuse the light a bit (for a low beam) at one focal point, then create a pencil thin beam (high beam) using another. This dual-filament design is imitated in some expensive HID retrofit kits that have both high and low beams using a single HID lamp and reflector. I thought of doing something similar with my LED headlight project, but I am waiting on the ideal LED emitter yet.
Unfortunately, this would be an illegal mod (for "off-road use only"). Actually, it could be dangerous since these standard headlights designed for dual-filament halogen bulbs may not focus properly with a crudely focused HID lamp. The glare could be blinding for oncoming traffic. If you are totally serious, I would closely study and measure the focal points of your headlight assembly (for the correct beam profile), and the exact location of each filament in you original stock halogen bulb (the one specifically designed to work with your headlight assembly). Even an incorrectly focused high-output halogen lamp could be as dangerous. If you can create a precise track system that slid and tilted the HID lamp to mimic the halogen dual filament bulb, then you might be able to get away with it safely after testing for safety afterwards. This is what I intend to do with an LED if I use the standard reflector assembly. The bulb can move along the carefully machined tracks if you use a servo mechanism or geared motor, a solenoid, a push-pull cable, etc. Make sure it is designed for long life in case it gets stuck in the "high" beam mode at an unsafe moment.
To make it easier on yourself, I would recommend just upgrading to a aftermarket projector headlight assembly. I mean the ones using an elliptical reflector mated with a condensor lens (like an aspheric lens). These are usually safer because glare is controlled better due to a built in shutter that creates the perfect vertical cutoff. For me, if I cannot get a modern "side-emitting" LED emitter that could match the light radiation pattern of a standard light bulb (which is what most shallow reflectors are designed for), then I may try to find a HID projector assembly and retrofit it with the standard LED instead. This would be safer, and the beam would be a bit more predictable.
I hope I was helpful. I guess that if you are looking for a cheap and quick fix, then please do not continue for the sakes of the other nighttime drivers. I really get angry when I get blinded by the ignorant people who place cheap or improper HID lamps in their old headlight assembly. The glare is terribly distracting, and sometimes blinding (even on split highways). With some time and careful measurement, you could make a simple, but precise mechanism that could do what you want for not too much money (if you are resourceful).
Cheers,
-Tony
