Cold turkey method works. They will eat Reptomin eventually, some take to it faster than others. It took me a while to get my frogs on pellets but they will eat them now.. they don't eat it with quite the enthusiasm as they do with frozen/live foods though..

I personally feed my frogs Reptomin ~75% of the time.

The rest of their diet is earthworms (which I have to cut up since my frogs are not adults yet.. and it is gross..) about once a week.
Hikari Bloodworms (once every two weeks or so).
PE Mysis Shrimp (about the same frequency of bloodworm.. rarely).

I've also fed my frogs thawed frozen pre-cooked shrimp once (no salt, spice, ect) and they seemed to really enjoy that too.