Second the glass bowl idea; I use them myself. You could also use a separate feeding container/tank - drop the frog in with a few crickets and let it feed for about 10-15 minutes before returning him to his cage. That way you can monitor exactly how much he eats. Not every frog will be comfortable with this method; but White's tend to be bold and voracious enough that a little traveling during mealtime should not affect their appetites. I do this with my gray tree frogs sometimes.

You can find red wigglers in most bait shops. Dubias are harder to come by locally; perhaps reptile shows; I actually found a source on craigslist once. If not, you can always order them online, assuming you are willing and able to keep them by the hundreds.