I bought one before seeing this, along with those excellent instructions (and I have one of those insta-cameras right over there. The viewfinder is really nice, but now I wish there was a way to turn off the live view when using it, and just have the info.
I didn't invented it, but when I thought about it and read this solution, I immediately tried : most people have the necessary parts in their junk box, and even if you had to buy a throw-away camera, you can't be wrong for $4 when comparing with the $100 a true olympus VF fetches.
The problem is the aspect ratio.
If you shoot jpeg at 3/2 then a finder is easy to get.
I wish my cameras shot raw on a chosen aspect. I'd be back to 3/2 in less that a heartbeat.
I would not use the VF1 with the 20mm.
You'll have cropping galore.
I use the 20mm with the voigtlander 35mm. because of the 4/3 format, the very top/bottom of the brightlines match up well with the final picture, but the sides will get chopped off. voigtlander also makes a 40mm viewfinder but it's 3:2, not 4:3.
my biggest problem with using the optical viewfinder is the slow focus of the 20mm, especially in lowish-light situations.