If you are going to go through all the trouble to setup a cron job to manage the standard backups, then why not just take over the backup process yourself and then you can have complete control over how many, their naming, their frequency, and just about anything else you can think of managing.
I wrote a post some time abgo for how to do this and it would take you about the same amount of time to setup as it would to start writing your own cron jobs to manage this stuff. My post also uses a single cron entry to do the same thing but with more options.
Read here:
BKM