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.