You could bodge them. I’ve not had much success with fillers (GunGum etc, always flakes off within a few miles)… perhaps try high temperature silicone sealant and wire some thin steel sheet (e.g. from food cans) around to hold the stuff in place, but it would only be a temporary solution.
Welding would require some complicated shapes to be fabricated to bridge all the wafer-thin bits so would end up being pricey, and chances are that the rot has spread beyond what you can see so even that won’t be a long-term fix.
I'd recommend some stainless ones if you have the budget for them.