My son was exactly the same and dips are a great idea for now, but maybe you should slowly introducing him to fruit and veg. We haven't got a very big garden its tiny in fact but i brought a few seeds we grew carrots, potatoes, cabbage and lettuce and he loved watering it and watching it all grow and then he couldn't wait to eat it and try what he'd made. Another thing that really encouraged him was I brought this blackboard that had pictures of veg on and asked them to draw their favourite and he really enjoyed doing that and he learnt all the names it was a great learning process.
He eats veg every day now so dont give up :)
Good Luck x
I couldn't upload a picture of the blackboard but if you follow the link you will find it!