CallingStationId

Hello, I finally have a working rp-pppoe+pppd+linux+radius+mysql setup handling lots of connections :) I used to handle pppoe connections on freebsd, and when a connection is established, the field "CallingStationId" of the radacct table on mysql had the mac address of the calling user. rp-pppoe (or maybe linux pppd) seems not to do this by default and the field in question is left blank. Does anybody know a way to solve this? Thanks in advance..