Maybe scroll to the point you want to rotate from, rotate, then scroll back. It may not work if the engine waits till the next frame to apply it. I haven't tried it though. Worst case you'd just not use the layer rotaion feature and rotate like newt suggests.
More general control for layers would be welcome. Instead of the parallax controls I wish layers could be moved, rotated from any point, scaled from any point X and y, and why not, skewed from any point. All those are affine transformations and it would make you and I happy to have.