Instead of trying fill in with solder between the ribs, Tom and taking the chance of getting too much heat there (barrel separation), I'd simply use JB compound. Leave a little bubble of epoxy sticking out and file it flush after it cures. If you want to file out a piece of aluminum or steel to fit and epoxy that in, that's a possibility as well.
If this shows I'm a 'hack' well, that wouldn't be far off.