If you have no dock for it, then your only option is AppleTalk/LocalTalk (aka serial networking through the Printer/Modem port.)

In order to do that, you will *NEED* another Mac capable of running OS 9 or earlier that has a serial port. Then you can turn on File Sharing, and share files from the other Mac to the Duo.

Unfortunately, it is EXTREMELY difficult to swap out the OS over AppleTalk.