The OP is not likely interested in monitoring software advocacy, he wants "a quick & dirty way to guarantee a good nights sleep" while his buddy is on vacation.
I still think a smart wrapper around check_tcp is the way to do this. Perhaps not out of cron, it can instead be a long running process in a sleep/fork/exec(check_tcp)/waitpid loop.
And that's exactly why you don't roll these things on your own unless you have a very good reason. Making sure a cronjob doesn't stack up reliably is non-trivial and becomes extremely hairy when the network gets involved. Many people think "I'll just use a lockfile" - think again.
Since for monitoring scripts this kind of reliability is the whole point, I strongly suggest to use something like monit where someone else has already worked out all the little corner cases.