@Copernicus,

The camera-ui is started (by Xsession) using "dsmetool -t /usr/bin/camera-ui".
"t" means "start-restart", i.e. on process exit it will be restarted up to N times.

So in principle killing it (after testing if it's actually running) with "dsmetool -k" should work fine (as long as you then restart it using dsmetool if required).

As an idea, perhaps SIGSTOP (and then SIGCONT) might do the trick nicely. But it's just an untested idea.

[EDIT] forgot to add, this is using CSSU-thumb, but was the same with stock firmware.