Just my opinion, you shouldn't switch them off live.
Remember all those HUGE Armatus we've seen, especially those out of the US? Most were fed live only, and from what I've observed, many Armatus that aren't fed live have died off some time or another(not to say that EVERY one of them has).
I believe that there is something in live fish that Armatus require. A part from the hassle of having to run to the store frequently(though here in Singapore it really isn't a problem) and the tiny risk of introducing parasites, feeding live has only benefits.
I'd try feeding large cichlids, I don't think it's easy to find live fish in the wet markets that are between 4-5 inches in length. I don't think it really matters which species you feed them, as long as they aren't dangerous in anyway.