You can use the Reset button once you have connected the Omega to the USB cable and opened the serial port, in the exact same way that you would use the power switch to turn the unit on. The same U-boot prompt will then show up with the 3 second interrupt window, a few seconds after you have pressed the Reset switch.
I suspect that since your Omega was not fully plugged into the dock, there was no voltage applied to the reset pin and it was never carried out.
If you're connected to the Omega via the serial terminal, you should see
Hi @john-b, Yes, there is a way for you to "make" your own ethernet expansion, however it is going to require some hacking, especially since you do not have expansion dock. The Arduino Dock does not break out any pins from the Omega itself, so as fas as flashing the Omega goes, it won't be able to contribute much.