I found and purchased an Olympus Fisheye adapter (FCON-T01) from B&H the other day and am very pleased with the results, More fisheye than I would like, but Less than it should be. I am still looking for a wide angle but no luck. They do make one for the Pen (WCON-P01) but I don't believe it will fit the 40.5 threads.
This one will certainly do until something better comes along. I see no degradation in the images and it is very well made. The multiplier is .74 which makes the 10mm 2.8 a 7.4mm.
Here are some images (very reduced resolution for publishing)