Diagnose misfires before the ECU codes them

My 2007 Mazda 6 ran rough for months before the check engine light finally came on and the ECU set a code for misfires on cylinder 1. Replacing the coil on that cylinder fixed it and it was running beautifully for a few weeks.

Now the same engine roughness is back, and no check engine light is coming on. I ran an OBD-II scan and there were no error codes.

Based on the previous behavior and the recent repair, if I were a gambler I would guess that the replacement coil has failed. But just to remove the manifold to access the rear cylinder bank costs at least two hours.

Is there an easier way to confirm there’s a coil failing without opening things up and swapping coils?