In my recent ploy to get downvoted, I'll sum up my view of this: Fuck you, pay me.
(Unfortunately from what I can tell, the studies on how different kinds of motivation [intrinsic, tangible extrinsic, social, etc.] relate are all over the map, and appear to depend sensitively on the specific kind of task and setting.)
Either by practise, or by some self-hypnosis-like trick.