i was thinking of contacting this guys about making a custom cpl lens attachment but i doubt he would help seeing as how the k1s community isnt very active and thats a big shame i really like the k1s.
Got one for an 0805 - crudely taped in place at present but am going to get some magnets to secure in the future. Had to trim some plastic back from the camera but works wonderfuly.
The filter I used was the same as the 0806 filter and I used a bit of rubber cut into a short length of tube to couple it onto the front of the camera barrel. Pics on that forum (it's a bit slow to load so be patient with it).