Invoking R from PHP/Mysql environment

We have a setup in which we use PHP (with Geeklog as a CMS) as a front end
to MySQL. We plan to use R for offering user driven and automated
statistical analysis of some of the data we obtain. We'll be using the R 
interface
to the MySQL database from omegahat (www.omegahat.org) for getting
the data out of the database, but we were wondering if somebody tackled
the problem of how to integrate R nicely with PHP.

Specifically, we know how to get R to run as a system command from PHP, 
but
ideally we'd like to call R as a PHP function. If somebody did this we'd 
like
to have some pointers as to how they did it If not, we'll probably do it 
ourselves
and post the results