Hi Bill,
I tried this example out. The call from TSQL works nice. 
But call it via JDBC
CallableStatement call = connection.prepareCall ("{call GetRPlotInHtml  (?,?,?)}"); 
                    call.setString(1, r);
                    call.setString(2, sql);
gives an error: com.microsoft.sqlserver.jdbc.SQLServerException: Unerwarteter "R"-Skriptfehler beim Ausführen von "sp_execute_external_script" mit HRESULT 0x80004004.
The user has the rights for any external script. 
Is this a limitation of R usage?
Joachim