Given the lake I'm guessing you were fishing, there doesn't seem to much aquatic life in the form of insects. Caddis flies is about all I've seen there. Had that been me, I would've tied on a good sized hopper with a caddis nymph. It sounds like he was probably eating what the carp rooted out of the silt and mud, which was likely caddis larvae. But, he also came to inspect your gurgler, which means he was looking up too.

I'd toss one of my foam boddy hoppers with a BH chammy caddis...

But then again, I like the leech idea too.

You never know, maybe that hold over would still take "fish food" too (i.e dog-food fly).