try offer something you think he will like next to the paste and gradually move on to more and more "normal" bites vs.paste.
Feed him when he is hungry and offer bites first while you are "grinding the rest". Sometimes I serve my kids their unfavourite food first while I am"getting" the rest. They'll sit and munch what is set before them. Try making it look appetizing
It might take time since it's a habit.