Hi Renee
It sounds like a "live trap" is your only option.Is there a group in your area that does feral cat spay/neuter?They might be able to lend you a trap.At the very least they will certainly give you advice and tips.
I recently traped a little pregnant mommy cat,who moved into my barn to have her kittens.and a wonderful "cat lady"gave me lots of good advice.
Good luck!I'll cross my fingers for you!