How long are the runways?
If that's no option I'd keep my student in the pattern and I'd be on the phone with the nearest ATC facility to coordinate radar vectors.
Mind you last job as flight instructor we'd solo at a different non towered airport. I'd instruct my student to fly back to our towered home airport and leave me to take a cab.
Prior to solo they'd have flown that exact route at least 5-6 times already.
Back and forth. They'd also know how to contact ATC radar so in the big scheme of things it really wouldn't be an issue.