Hm... Completely not frog-related, but have you tried frozen/thawed silversides for your turtle? They come in a plastic bag you can stick in the freezer, and can be ordered online if there's no petstore nearby. I rescued a box turtle last summer, and she loves them. They'd work fine for sliders too. Plus, if you chop them up with other food, the smell will usually convince even a picky turtle to eat new things.