Bind the rowsource to a query with the following output, in this order:
Contact Title-Contact First Name-Contact Last Name
Set the bound column to be 3 (that's the SupplierID)
Set the number of columns to be 3.
Set the listwidth to be, say 3".
Set the columnwidths to be 0.0007";2.9993";0
0.0007" seems to be the smallest column with the combobox control can use, and still recognize it as a column. But at that size it is effectively invisible. So, when you pull this thing down, you will get list of supplier names, but when you let go, the display will show your catenated contact field. The bound key field will remain hidden through the whole process.
Basically, the Access combobox will display the calue in the first column, but you can hide that first column from the pulldown by using this trick.