It looks like you also might have a problem with the lead singer's mic cable intruding into your (screen) left crop...
From what I can see, rotoscope (in the sense of precise, keyframed masking) is not going to be necessary here; you just need to draw a feathered bezier or b-spline to mask out your trouble spots.
If you take the keyboard player's shadow as an example, I'd image if you feathered that out it wouldn't be too noticeable as being cropped. At least you have the advantage of a single-point light source so if you shorten the shadows it just looks like this was shot closer to midday
If I can humbly venture an opinion, if the rotoscoping were needed to fix a shooting issue caused by me (or someone in my employ) I'd be inclined to swallow that cost.
If you're wanting to fix this in FCP (as opposed to AFX or Motion) because you're concerned about its effect on your Color workflow, I'd suggest:
Sending the 3 angles separately to Color (lay them end to end in your prep sequence)
Grade them the same (copy the grade to each) and them render them out (maybe with handles just in case)
Then you can do the comp after the grade (AFX or Motion).
Hope this helps.
P.S. And I know this is advice after the fact but you could have changed the angle of the shadows by rotating the performers and moving the camera.