Okay, so I've made a bit of headway... not as much as I would have liked, but enough that I think this is definitely the way to go.
Here are the plastic balls I ordered. Two 4" and two 5".
I cut them in half and cut circular holes in two halves for the projector lens, and another hole in one of the 4" pieces for the back.
Here is the 4" on the front:
And the 5" on the front:
When trying to fit the above two pieces into the stock reflector housing, the 4" seems to small and the 5" too big. I think I may end up using some mold-release compound and some super heavy-duty epoxy at work to build up the area around the stock reflector to make the 4" fit nicely. That will also give it a better seat.
Here is the back piece. When it is ready to fit, I will glue it to the back of the projector and seal it.
The idea is that the projector will basically be sandwiched between the stock reflector and the back half of the housing. Below is how it would sit against the back of the housing. I want to make an insert in the hole to hold a large-diameter o-ring in order to create a seal while still allowing the projector to move.
There are still some hold-ups with this idea, but I think this is a better way to go.
If anyone sees anything catastrophic that I'm walking into, please let me know, or if you have any good ideas too... I promise I'll credit you when I write the DIY
Jason