I think you can do what you need but it will take using a 2.5mm
stereo male to male cord, coming out of the
shutter remote jack.
You cannot use the hot shoe or PC cord jack because these are deactivated above 1/180 sec. I will test it once I get the right cable.
I have tested it by plugging my remote release cord into the cactus clone triggers I have, and depressing the button on the remote all the way down will trigger the cactus.
You can mount the cactus on the hotshoe of your K-5 for convenience, but you need to insulate the contacts with a piece of electrical tape so the camera doesn't think you have a flash on it.
The cord I think will work is this one.
Angled 2.5mm Stereo M / M Mini Plug Patch Cable 1.5 Ft 670561989054 | eBay
EDIT: I took apart my remote switch to test my theory and it is inconclusive.
I used a continuity tester to see if i could get a signal at the two points when I depressed the shutter on my K-5 and I don't get a reading.
I'll order the cables and conduct a test when they arrive.