Is there a fitting OP reflector or do I have to sputter it myself?
Mikael
Don suggested hair spray on the reflector.
I used diffusion film on my Z1, easy, cheap and happy with it, plus it's reversible.
apply to lens
it is magic 
Obviously one piece of tape won’t be enough to cover a lens wider than 3/4" in diameter. Does the seam show up at all when you butt two strips side-by-side on the lens?
Not sure, I'll try it later. I doubt it. I've only used it on a couple multi-5mm led work lights that had way too much throw - it doesn't show at all on those and I made it overlap on purpose.
AH-HA! So you admit to using those multi-LED lights! 
-Garry
oh yes, I have several...for some things, they're quite good - ex. ceiling of my truck cap...
In fact, I've even modded them. no way I'm posting that stuff though 
Here's some pics of citipower x5 (p60 xml) - stock, with tape and a view of the tape (blurry pic, but it overlaps in the middle)
Window frosting spray works great .
Probably better - I just don't have any. I did consider lightly bead blasting the clear cover on my multi-led work light but the tape was so easy.
This is one of the things I'd like to test w/ I.S. - actual losses w/ different stuff - since I like diffusers...
What about spaying with a "clear coat" paint? Doesn't Old-Lumens do that? Hope so, because I picked some up for this purpose.
-Garry
DCfix seems to work best with the least loss of light.
If you PM me your address, I will send you a flat envelope with some removable diffusion material to place on the lens.
Mikael - take him up on his offer! The diffusion film is the best - has fixed ringy beam on two of my flashlights. Easy to apply, easy to cut and easy to remove if you don't like it. (Thanks again, Chicago X.)
Dave