Anything is possible. You could add an external Ethernet controller to the Mini-FlexBus. You might be able to find a USB-connected Ethernet adaptor. But you can't get Ethernet on that chip without external hardware. Any "non-standard" solution would make the software a lot harder to get working.
The only MCF51 chip with Ethernet is the MCF51CN128. That has half the FLASH, less than half the RAM and a different mix of peripherals to the one you're using (no USB for instance).
You may need to step up to an MCF52 series chip.
Then you'll need a lot of extra software to get the network stack (e.g. FNET) unless you're already using something like MQX.
Tom
