If I have enough bait that I feel like saving it, my method is pretty simple.

Line the bottom of a bucket with newspaper.

Dump the minnows in.

Sprinkle them liberally with salt.

Let them gasp and die and dry in the sun until the newspaper is dry.

Put in a bag and freeze.

They are slightly leathery when you put them on a hook. They don't stay on the hook as well as fresh ones, but pretty well.

It's a cheap simple solution. If the perch are hungry they bite on them just fine.