RADIUS MAC authentication Accounting problem

Hi

Using Mikrotik v2.9.24. I’ve enable the RADIUS MAC authentication under the wireless security profile. This sends the mac address as a username to my freeradius server and blank password. Authentication is happening from my wireless clients, but i’m getting no accounting from the session. Only if i do a PPP over wireless connection (after the successful MAC authentication) i start seeing accounting in the radacct table in freeradius. Any idea how i can force the Mikrotik acting as a NAS to send accounting details to the freeradius server by doing only RADIUS MAC authentication?

Thanks