On this page
http://www.asteriskdocs.org/en/3rd_Edition/asterisk-book-html-chunk/database_storing-cdr.html
You can see how to use multiple backends using multiple stanzas in res_odbc.conf , in FreePBX you can effectively do that by adding another [asteriskcdrdb] to res_odbc_custom.conf which would refer to another connection in /etc/odbc.ini
The remote server can be any odbc compliant system , not restricted to MySQL , itwill need a user with necessary acl’s to make the connection and a destination the correct tables with columns that match the table and aliases . This is all better covered in the link above.