I baffled my penguin filter but I did it a little differently.
Sponges, even aquarium ones, freak me out a bit since I know many of them are treated wish various chemicals and anti microbial solvents, etc etc. I didn't want to risk poisoning my tank with one, so I used old filter floss from the cartridge previously in the filter and cut it to size, then put a rubber band over the outflow and rolled the flap of floss around the rubber band. It created a great baffle that won't slip, used a piece of media that was already aquarium safe AND had beneficial bacteria in it, while cutting down on almost all the current.
Filter floss is very permeable, but it is enough interference to really slow down the sheet of water being spewed out by my bio wheel :)