One of the special thing that guppies bring to the table is the water they come in from the pet store. That is powerful stuff and shouldn't be taken for granted. When I'm trying to switch a guppy only eater over to worms I use the wonderful fishy water to my advantage. In with the guppies I add my small worms and just a dash(bam!) of guppy water. That fish smell overpowers the worm smell and most of time the snake doesn't know the difference between a worm piece and guppies.
Doing this only once has converted many of my radixes over to worms when before they would only eat guppies. My last convert was a little snake I call Funny Face. He has a facial deformity on the right side of his face that involves the upper lip and eye socket. He was a guppy only eater until the other day. Now, he's out eating worms with the rest of his siblings.
It's guppy power only in a liquid form.