I've been thinking it would be handy to be able to bend a simple shape by a specific angle. Tried using the warp shader and got a pretty good result, but the problem is it skews shapes instead of rotating them.
So here's what I've come up with so far. It's ugly but it seems to work, though I haven't tested it in any real scenes yet. Basically it breaks the shape into two halves (at Z = 0), rotates the positive half, then pastes them back together. The X and Z positions have to be manually tweaked to achieve a good fit. The result can be then rotated and placed freely in the scene.
There must be a more elegant way to do this.