I went to Home Depot at lunch and bought some 2" ABS plumbing fittings. I'm about 90% certain I can make an adapter that will work. The inside diameter of the fittings is just over 2 1/4" while the eye piece of the Leica is just under 2 1/4". The focus ring on the RX100 at the base of the lens barrel is also about 2 1/4" so I should be able to use some of the loop side of velcro to fill the gaps and snug everything up so the only challenge I'm expecting is getting the camera lens the proper distance from the eyepiece but that really shouldn't be too difficult.
I spent less than $10 on pipe and fittings and if I knew for sure the exact parts that are needed it probably would've cost less than $4.00. Assuming I'm successful I'll post pictures of the adapter.