Call me crazy (everybody else does). It would greatly complicate the build, but if you left the forward ends of the outboard open (or put small central ramjet partial cones it, leaving the partially open just like a real spike nozzle) AND you ducted the flow INTO the core tube, you COULD Recess the motor at least half a main tube width, maybe even more, as it WILL act a bit like the Lil’Augie. So you could actually have some useful function from your simulated ramjets.
also agree with
@techrat , even completely open those tubes are far too long to function as tube fins and would act like solid cylinders or worse.
@neil_w , is there a maximum length To diameter ratio for tube fins beyond which they completely lose function?