background fsck service - any tools?

Is there any tool that will unmount a filesystem and fsck say once every 2-3 months to avoid having the massive slow fsck on the reboot every 6-12 months? If not I am thinking of a cron job that tries to umount the filesystem in the middle of the night, run a basic fsck and if all goes well remounts it mailing the results to root. I have a modest root/usr partitions but the larger other partitions only used for recording TV take 30+ minutes to do the occasional fsck and that always is demanded sometimes very inconveniently on a reboot. Andrew