Maybe just run an extension cord to the fridge?

As others have said, that adapter would not be hard to make. Amazon sells an L4 to L14 adapter for the same purpose. There is possibly one available for 1 or 2 Nema 15 inputs. Or get a Nema 15 to L4, then use this L4 to L14 adapter.

The issues is that somebody doing this is going to be tempted to pull more current than the generator can provide. It doesn't seem like a good idea.