Customer Item Xrefs shared across multiple customers

 We have a requirement where some groups of our customers share customer part number cross references. 

So customers 1, 2 and 3 may use a cross reference ABC123 which represents INTERNAL item XYZ. 

However in the customer items table it appears that I have to set up the customer item three times (once for each customer using the cust. part number).

Is there a more efficient way of handling this? This is becoming a maintenance problem for us, since in some cases there are 10s of customers sharing the same part number (about 3000 parts).

Thanks for any insight.

Nat.