I have also read about this.
And I plan on doing the same for my packman frog.

But I haven't heard of putting a live insect in the casing.

The ingredients I have seen used vary greatly.
From found up dog food cooked beef heart, liver , chicken ect ect all kinds of sources of proteins.
Also he made two different batches.
One batch that has calcium supplements and the other batch that has multivitamins.

Then he would freeze them and thaw them out over night and put in warm water for 10 min before tong feeding.
and for the more stubborn feeders he would loosely tie the sausage to a dark thread and drag or dangle it above the frog.