I’ve used a few methods to use a fly with a spinning rod.

Bobber/bubble with a fly
Drop shot
Tying flies on jigs

I prefer size 10-8 or 1/48 jigs for bluegills. Almost any old nymph will work, really. If you squirt a little slab sauce one them they work even better.

You should consider getting a fly rod and learning how to cast it. It is really a better way to throw flies. Fly casting is not that hard, and doesn’t have to be expensive. Although it probably will be expensive over time.