It's been requested many times and finally we've done it … you can now use SQL Server Stored Procedures as a Read-Only Data Source in Data Sync release 3.0.882.
Simply enter the Stored Procedure in the Command or SQL Tab of the connection using the keyword EXEC to indicate that it's a Stored Procedure.
Because stored procedures can return different results depending on the parameters passed it's difficult to get the schema. We have to execute the Stored procedure so we do this in a Transaction to rollback any changes to the DB that may be executed. Therefore you can use Temp tables and the like in the Stored Procedure but it might take a while to load if it has a lot of work to do.