It's impossible to restore backup to previous version

>I need to "copy" customer database to my SQL server 2008 database. My SQL server is 2008 (10.00.5500) and the customer's is SQL 2008 R2 (10.50.1600). Of course when I try to restore their .bak file I get message that it can't be done.
>I am concerned that upgrading my SQL server to R2 may not be practical. Can anyone suggest an alternative way of accomplishing that task? TIA