Thanks for the suggestions everyone 
I figured if I'm going to replace the panel anyway, I may as well attempt to short out the damaged cell. I drilled a couple of 2mm holes near the (visible) bus bar on each edge of the cell, erring towards the damaged cell (don't want to drill the good cell next door). Then used the edge of a file to remove the top encapsulation layer from above the bus bar until the metal was exposed. Then I got some ~1.5mm diameter solid enameled wire (I forget the current rating but it was plenty), inserted from the underside of the panel and bent 90deg such that it sat nicely on the exposed bus bar. Then soldered to short the cell. Seems to have worked nicely - output is better than it was before and the damaged cell no longer gets hot. It was hard to get a good solder join to the bus bar. Hopefully it wasn't a cold solder join that might just crack off - time will tell. Got a few hundred km on it now and it seems ok though.
I figured if I'm going to replace the panel anyway, I may as well attempt to short out the damaged cell. I drilled a couple of 2mm holes near the (visible) bus bar on each edge of the cell, erring towards the damaged cell (don't want to drill the good cell next door). Then used the edge of a file to remove the top encapsulation layer from above the bus bar until the metal was exposed. Then I got some ~1.5mm diameter solid enameled wire (I forget the current rating but it was plenty), inserted from the underside of the panel and bent 90deg such that it sat nicely on the exposed bus bar. Then soldered to short the cell. Seems to have worked nicely - output is better than it was before and the damaged cell no longer gets hot. It was hard to get a good solder join to the bus bar. Hopefully it wasn't a cold solder join that might just crack off - time will tell. Got a few hundred km on it now and it seems ok though.
