Multipath -- Ignoring internal disks

I want to configure multipath such that it ignores all the internal disks and only sees SAN Luns. Any idea how can I achieve that? Basically I want to filter out all the internal disks like IDE, SAS backend etc except for SAN Luns. -- Using find_multipaths is not an option for me as I want to use multipath even when single path to a SAN Lun is present. -- Black listing based on device(vendor/model), wwid etc is also not an option as it is possible that I can have internal drive(s) as well as SAN LUN from the same vendor. -- I tried black listing using properties but could not find any property that will distinguish between SAN Luns vs internal disks. Any thoughts? I am new to the Linux internals. Thank you