Side plates, that's only thing I know of that's really going to be much thinner.
Grips are made for your type of grip usually. Higher wrist or lower wrist.
Ultraview makes a nice grip for the engage, so does Shrewd. The Shrewd might be just a little thinner. But they are all pretty slim, not talking much difference in them.
Looking to change my grip out as well. Going to try shooting off the riser and tennis racket tape first. If I dont like either of those then maybe try the side plates or ultraview grips.