Setting ON-NET status using DHCP Option 224 with multiple serial number

I have been able to successfully set the FortiClient On-Net status using our Windows 2008 DHCP server using the DHCP option 224. Now I need to support two Fortigate 60Ds that register our FortiClients. Does anybody know how to enter two serial numbers in the options string field? I have tried using a space, comma and semi-colon as a delimiter.

Thanks,

Dave B