I used one of these:
Twin1
Although they do make one for the Pentax ... it just uses the IR remote ... and also a cable as well.
all it uses is s 2.5mm stereo jack (both ends) and plugs straight in the side of my K10D behind the door.
The IR remote works nicely with the 3-sec IR remote delay and can use the AF prior to taking the shot as well.
Also with the cable in place and hooked up ... Bulb mode works well (with a half shutter setting on the side prior to truggering the shutter) ... button on allows half press AF as well with cable in place.
And it wasn't too badly priced either fro my local camera shop ... was $40AUD. Which to me was cheap anyway.