Got curious and was able to hack my way to adding a Pan parameter to all the Synth glyphs - Shrine, Topiary, Vale. Just crawled through the scripts and found anything similar to velocity and duplicated it for Pan (except where it related to a MIDI glyph).
Only unique pieces were basically setting the pan ranges from -100 to 100 in the pan mixin, adding engine.pan(x) to the sound:play() call, and passing cell.pan/100 into sound:play() since the engine range is really -1 to 1.
Not extensively tested but worked for the jamming I did, even with Cloakroom modification of the Pan param.