BUMP. I would like to know as well. Just looking at it, I would say the existing eye cup is not detachable by any means that wouldn't cause damage. So, something must be able to fit securely over it.
I just took the circular eye cup with a rectangular base off of an old Canon AE-1 SLR. It's the right size opening (won't fit over). What I did notice is that the added mm's of distance really increase the tunnel vision and make it hard to see the EVF.
Given that result, I'd say that anything that would fit over the LVF1 would need to essentially be flush (or almost flush) in order to maintain a good FOV within the LVF.