If only using the curl circuit for the sickle bar mower, and no bucket operation, you would use one hose in one of the curl work ports. Run the other work port hose to the return port for the time you are using the sickle bar mower.
If you will be using the bucket with the loader, then you will need a diverter valve that will shift the fluid to the sickle bar mower using a switch on the handle. Even using the diverter valve, you will still use one of the work ports for the sickle bar mower, and run the other work port hose to the return line.
A diverter will run about $95 to $200