Hi Eris,
I know that Winamp/WACUP doesn't provide direct stereo channel support. In some cases, the mono data provided can be made to simulate stereo. The simulation is not 100% accurate, but it's better than nothing, imo.
What I did with some skin scripts (that exposed their control logic) is duplicate the applicable control section and added an additional timer (so that each section has it's own timer). Then I slightly adjusted the responses frequency ranges for 1 of the control sections. Finally I assigned 1 section to the left channel and the other to the right. This is what I referred to as a 'fix'. I should have said a 'work-around'.
The control logic is not the same in every skin, but I've been able to apply the basic idea to exposed control logic for some visualizations and animated speakers. I can pm you examples of what I did, if you want to see them.