Sounds good. Just freeze them whole at 0 degrees celsius or below. Leaving them frozen for several weeks ensures that most, if not all the parasites will die.

Be sure to thaw them completely before feeding them to your snakes. If the frogs are too big for your snake, you can always cut them up for smaller snakes. Also, taking the guts out will remove many harmful parasites that live in the frogs digestive system, such as tapeworms and liver flukes.

If you have not treated your snake for internal parasites, then chances are he already has them. This is normally not a problem for a young healthy snake. It can become a problem if your snake's immune system is compromised by old age, stress, illness, etc.