Drill a 1 inch hole in the center of the housing. This will allow the HID bulb to fit after you install the lens.
Remove the unused wires from the rubber boot, install the bulb and install the boot in the housing.
Install the lens back onto the housing, carefully pulling the wires out the rubber boot at the same time.
The HID bulb fits right in the rubber boot. Use silecone to seal the holes in the boot and around the lens, so water and dirt is kept out.