Adding custom data into Piwik from a database

I would like to to use Piwik to track certain metrics grabbed out of my webserver’s database. For instance I’d like to keep track of how many users my site has. I can gather the current data by doing the following mysql query:
SELECT count(*) FROM Users
What’d I’d like to do is something like a cron job that runs every 12 hour with that query and sends the results to piwik so then I can track that over time and see graphs regarding this.

Can someone explain to me how this is possible or point me in the direction I need to go to learn how to do it? Thanks!

Maybe this isn’t possible?

Check this out: How to write a Piwik Plugin