Hero / Hench speech bubbles

Is there a way to turn them off?

Not that I'm aware of.

damn they're annoying on a small screen!

You can alter much but if its not in the options there is little you can do so far as I know.
I don't think they come under dialogue so you couldn't turn them off on the interface.

Does altering the interface size to small help by reducing them or can you run in a higher res, though I am guessing you have tried all this already.