Usually, those are notated just with text placed either above the staff or between the staff lines (for a single organ stop). The normal stops only take a few

Usually, those are notated just with text placed either above the staff or between the staff lines (for a single organ stop). The normal stops only take a few characters to notate. More modern music for more complex organs will include a small amount of text indicating when to change between stop configurations or sets of manuals that are preset. I can't imagine it would be that hard to notate such things for electronic music. Good old text sitting next to your good old staff works wonders. The bigger issue for electronic music, IMO, is the notation of sounds that don't fit on a staff well. Modern classical composers (who use sheet music extensively in the creative process) have various notations for these sorts of things.