EAP checking certificate CN for WiMAX

Hi, In WiMAX certificate CN apparently contains MAC address and model name of the device for example "FF1234567890 USB1234". WiMAX standard says and I quote "The MAC" (from the CN) "SHALL be compared with the MAC address in the Calling-Station-Id of the RADIUS Access Request message. If they do not match the authentication SHALL be rejected." I tried to use "check_cert_cn" inside eap.conf this way check_cert_cn = %{Calling-Station-Id} obviously doesn't work because the CN also contains Model name check_cert_cn =~ /^%{Calling-Station-Id} .*/i doesn't work as well because of syntax error is this the correct way or there's a better way? Thanks for your help. Victor