How to use conversation without any port_type defined ports

Hello all,

I have my own protocol what lays direct over ethernet. My dissector gets called over an defined ethertype and here is the problem.

My protocol has a 4 x 8 bit header ... one field is a unique number.

The header looks like this ethernet [destination address(6)][source address(6)][ethertype(2)] my protocol [my protocol field one(1)][my protocol field two(1)][my protocol number(1)] [my protocol field four(1)]

I would like to use the conversation_xxxx() functions on "destination address" and "my protocol number" is this somehow possible? Or is there another way, perhaps entering a custom port_type.

Thanks Gath