Oh, sure enough, found the upload page on the Netgear firmware on my second look. I just missed it the first time, thanks! Got the image uploaded through the ethernet link and all seems well. 
I'm back and need a little more advice. I can't seem to get the R7800 with OpenWRT/LEDE to connect with my Frontier FIOS service. The WAN just keeps showing not connected. If I switch back to my ASUS RT-N16 w/Tomato it connects instantly. They're both configured to use DHCP on the WAN port, there aren't really any other settings I can think of that would matter. Any suggestions? Or should I start a separate thread for this since it's more of a support issue?
New thread would be best.