The 4mhz clock won't give you very good resolution. You could average a couple of soft loops like Pommie said, on either side of 55khz to give you the appearance of doing so.
Another option is writing a value to the OSCCAL register to fine tune the output on the GPIO pin. If you don't write down the factory OSCCAL setting. Or, if don't have a way to reestablish the OSCCAL value like provided on the Pickit 2 programmer, THEN DON'T DO IT!!!!!! Don't blame me if you brick your 10f204.