Dear Nicholas,
I think you should describe the functions for Ag and Ag-Cu in a similar manner.
Just let them have some unique reasonable names ))
Then use these functions for building the setfl-file that for 2 element system has the following structure
1st element embedding function
1st element density function
2nd element embedding function
2nd element density function
1-1 pair potential
1-2 pair potential
2-2 pair potential
Hope it helps!
Vladimir