There doesn't seem to be separate signals for each molten plastic recipe.
Thus one cannot use Set Recipe to tell an Electromagnetic Plant to use molten plastic when producing red circuits.
The only molten plastic recipe biochambers can have Set Recipe on is yumako+bioflux+calcite. I have Lignumis and Pelagos installed, so there's Cupravidis Necator and Methane-based recipes, but those can't be set by circuit because of this.
