In J1E, open the Attacks window under the Tools menu (or just press F3). Find an Attack that you want to use an event for, and for (at least) one of its bullets, set Gravity to 4 and Sprite to the event ID. Now you and enemies can fire carrots, floating platforms, shields, other enemies, or whatever else strikes your fancy!

DD's JJ1 instructions hint at this but don't quite make it explicit, so I thought I'd post in here to inspire people to make more JJ1 levels.