What about the following "workaround":
- you/or your plugin: saves the demos to e.g. /home/user/www/demoXY.dem
- your Webpage (e.g. php): manages the files (delete, compress etc.)
Requirements:
- webserver with php installed
- some basic experience in programming (e.g. php)
That's all. Of course you can set up an cron job.
More info about cron jobs you can find here:
http://www.scrounge.org/linux/cron.html
I hope I could help ;)