Hello JMB ZFT and welcome to the forum!
Nope, that's not possible. You have to have the cable to do the Bootstrap gig.
The unit is locked up if you have to go this way. Means it doesn't recognize the SD card. The only way around to unlock the unit is to "remotely" reset the unit with the cable and your PC.
I know this is uncomfortable, but better than sending the unit back to Humminbird.
Good luck and best regards / Harry