Hopefully not from your LFS, if so you have just potentially introduced pathogens to your tank, and new fish. Not good from a overall risk factor, and not good from a dietary standpoint. (if that was your intention?)
Don't allow the fish to train you, pick a quality food & stick to your guns.
Over the next 24 hrs slowly increase the temp to 82F. The rise in temp will increase the fishes metabolism, which will stimulate his appetite.
Make sure that you have plenty of surface agitation at the warmer temps (for 02 exchange), which shouldn't be a problem with your filtration & powerhead. If need be, take it to 84F for a few days, it won't hurt your fish, and may be the kick start that it needs to trigger a feed response.
Once he's eating on a regular basis, slowly decrease the temp to 78.