@dane-zone Yes scriptnode is probably the easiest way to go here, and there is an example implementation of a vibrato in ScriptNode here: https://forum.hise.audio/topic/4952/scripnode-101/13
Modulation signals don't produce sound, they modulate an audio signal, so stereo modulation is not possible.
Vibrato is just modulating the pitch, so unless you wanted to modulate the Left and Right channels separately there is no reason to process the channels differently. If you want to do this then follow the vibrato example above, separate the left and right channels, and add independent mod sources and delays on each channel (Left and Right).