I found this in the manual under "Stage":

The following stage either renders the whole scene again (PROCESS_TARGET not set), or only the TargetMap (PROCESS_TARGET set) for 2D postprocessing effects. You can use pixel shaders for 2D postprocessing, but no vertex shaders.

It seems to imply that 2D post-processing effects can be used, but I don't know if this would apply to panels or not...

I'm not too familiar with using views/stages/etc... any help would be appreciated.