How do I reference a Smarlist driven from members in a member formula?

I have a smarlist that's populated from members. I can reference it in a business rule using a planning expression like:

IF( "Product Channel" ==[[Channel.Retail]] )

The trouble is that I need do reference it in a member formula but Planning expressions are not supported in member formulas. The numeric ID value is not available (at least not directly) because it's a member driven smartlist.

There must be a away but it's not coming to me.

Thanks