I'm glad you got him mostly cleaned off. With any luck, his poops will fall normally again now.
As for getting him to try fruits and veggies, after a year of trying various foods in various ways, I took somebody's advice here and chopped up carrot into little bitty pieces, almost as small as seeds, and scattered about a teaspoon full on top of the usual seed mix in the usual food dish. And they ate the carrot!
Fresh carrot is a good choice to start with because it's a little sweet, it's a bright color, it's firm, and it doesn't go bad or brown in an hour like some cut fresh foods.