..Do you really need a ballhead for a monopod? I'd assume some sort of QR mechanism would do for you to quickly take off the monopod. The 70-200 has a dedicated tripod ring already, mount that to a QR plate, and mount the QR plate to the QR mechnism put on the monopod and it should be good.
In fact, you don't need a QR plate to shoot. Just mount the tripod ring to monopod can le.
I think a simple tilt-head would suffice if you need any movement from the support. Usually you'd use a monopod on longer glass with a tripod ring, so for moving to portrait orientation, it's really quite simple.
However, to give you a quick answer, you can try using your ball-head on the monopod. I believe it will fit, but the flexibility of movement (virtually all-directional) may get to you after awhile.