The move would benefit him more than anything. Remember that he also should have a gentle filter and an aquarium heater.
~Allowing the five gallon to sit for a couple of days while the betta stays in the 1/2 gallon is pointless. A five gallon has more room for waste dilution than does a 1/2 gallon. Just set up the five gallon, condition it, and add him in.
-Skip- The title of your question was "My beta fish always looks dead?!?", not "My betta fish is a happy little guy". Why should your advice be followed?