I have not tested this, but I believe to change what is returned by @@SERVERNAME, you go to
1) Failover Cluster Manager
2) Expand Services and applications on the left pane
3) Click on SQL Server on the left pane
4) Right click/properties on the SQL Server under Server Name, in the main pane
5) Change name under DNS Name
6) Restart of services may be required.
I feel bad showing an untested solution..but maybe I can help someone.