for a k750, make it a w800 and it will suport flashlite, but only on firmware R1NL... (I don't know the name exactly), but this firmware has a lot of bugs, so I don't recommend it
for k800/k810, put a firmware of w850 or w880 to have flashlite but if you'll do it, the joystick, camera and some others won't work, so I don't think it's worth
and now, the k850 has been released and it supports flashlite...