Sponge filters

You absolutely can. Many of us have used a coarse sponge (like those designed for Aquaclear filters) - just cut an 'x' down the centre, through the sponge long ways, and you'll be able to slide it over the intake like a sleeve. It's brilliant for keeping your filter media clean, as it catches all the little bits before they can get into the filter.
I once used one of the blue sponge filters designed for fry tanks, but found the sponge was too fine. The coarser sponges don't clog as easily - you want to catch the dirt but not impede the water flow.

I do the same thing with penguin reverse flow sponge kits. I am also using some of the lustar Hydro sponge filters. . They are much finer, but they are also stackable, so I can run a huge surface area, and not have to worry about them clogging quickly. I use the hydro sponge II size the most, it is small enough to hide easily, but big enough to do a good job. For my Emporer, I use Big Al's bulk sponge, because it is black and hides better. The ac sponges work fine, but I'm not fond of the yellow/white out in my tank.
dave