automatically add new Line to Graph

[blubbersuelze]

Hi,

i want to build a template which graphs the used Discspace of every userdirectory together in a single RRD.
The Problem is, i don't know (and i don't even want to) how many users are there.

To get the Data and send them to Cacti is no Problem, but i don't know how to build the Data Template and Graph Template.
Because at Moment there are maybe 10 Users ... next week maybe 12, or 14? ... in one month, maybe only 8 left ...
so the RRD should automatically be enhanced from 10 Lines to 12 or 14, and in a month for the actual view reduced to 8.

In know Monitoring Systems in which this is possible, is there also a way for this in Cacti?

thanks for help
blubbersuelze