Don't know your set-up, so this may not help much...

Can you place the taller plants to the right, and keep the light to the left, and tilted? Would end-up side-lighting the taller ones, but it may buy you enough room to finish without topping 'em, and side lighting still keeps 'em going. (albeit a tad crooked)

I wouldn't keep topping them as needed. The stress could force 'em into hermaphrodism or death. No chance of bending and tying the tops down a bit? At 4 weeks into flower, might be a tad tricky, and the top may snap off. If it does, keeping it as a clone is an option, but it will take longer to revert back to veg cycle and to take root.

Cutting a hole in the ceiling for more headroom isn't an option, huh...?