A.H.
Since you already have a marble jar, set up a new one. For every food he tries, put in a marble (or pebble, or whatever) towards a really big prize that he wants. You can decide beforehand with your husband what prizes are acceptable, and give him these options. When he chooses one, plaster a picture of that prize (like, say, Disney World for a whole week on his birthday) on that jar. So he will have a goal in mind for trying new foods, and you will have a way to get him to try new things.
Hopefully, the idea works for you! Best of luck!!!