Stay clear of those feeding blocks, those things are absolutely horrible. Whether they're eaten or not(from what I've ready they're rarely even touched), whatever is left of them will just foul up your water something fierce and since bettas are opportunistic feeders(that lack that "I'm full I should stop eating" switch), it'd be very easy for him to basically eat himself sick if he DOES eat it. They're just an over-all terrible idea, nothing but a marketing scheme.
Both your betta and your frog should be just fine without food for four days. As my dad always used to say; a hungry fish(and frog, in this case)is a happy fish. Just feed them both normally and preform your water change right before you leave, then return to feeding them normally when you get back. ;)