As an alternative to the passenger-mem-patch (http://code.google.com/p/phusion-passenger/issues/detail?id=201#makechanges) I've added a --kill flag to passenger-memory-stats.
Passenger-memory-stats will send a SIGABRT to any passenger-instance using more then the specified memory. This can be ran in a cronjob/watchdog fashion, where STDERR will receive output on a every process killed.
Abort passenger instance on high memory usage.
Yes this could be very helpful (especially @ night ;))
Phusion Passenger Enterprise already provides a better alternative. :)