Hi Aries,
this can be achieved by using the StereoFX effect with a random modulator in its modulation chain - you have to turn the Pan knob to the right to map the modulation from 0...1 over the complete stereo image.
Unfortunately, I forgot to add a simple line in the StereoFX code (I didn't use it for a long time) so it crashes the current 1.0 version. I've just commited a fix in GitHub so if you know how to compile HISE yourself, you can use this - otherwise you'll have to wait until 1.0.1, which is due in the next days.