Y'know...none of "Journey To The Swamp," "Save Your Chap," "Clerical Robes," "Ring A Bell," and "Enhanced Fertility?" are classed as Main quests, but are still needed for advancing the Main. Maybe do that with "A Date With Beth," re-class it as Side while still needing it to advance the Main? If that could be done (dunno if it's even feasible) it could be simpler than building in a new reason to learn Summon.
EDIT: "Find The Poacher," "The Peddler's Fate," "Clear The Mill," and "Flour For The Baker" are also Side quests which are required to advance the Main at various points. And technically "Speak To The Villagers," to even start the Main.