A previous study by Ackerman & colleagues (pdf) had a similar finding, but showed that you can also get the opposite effect, vicarious self-control depletion: imagining someone else exercising self-control can reduce your own level of self-control, just as engaging in self-control can deplete your resources for further acts of self-control.
They argued that you get vicarious depletion if you put yourself in the other person's shoes and take their perspective in imagining their act of self-control, but you get contagion if you just observe them exhibiting self-control. So I guess if you're watching tv for a self-control boost, don't choose a program where you get too wrapped up in identifying with the characters with willpower.
Thanks for the info and hrm... I would have thought imagining oneself doing it would almost act as "practice", rather than having the opposite effect. Oh well, and thanks, good info!
Just saw this article on reddit and thought it would be relevant here: Self Control is Contagious, Study Finds
Apparently seeing other people exhibit self control or even just thinking of them tends to increase (or decrease if observing poor self control) one's own self control.