The little round sponge made by Fluval you can just stick over the filter intake, it should fit over it and stay just fine on its own. It'll slow the outflow a little, but not by too much.....so you'll probably need to baffle that too. Just pick up some other filter sponge, the ones that come in flat pieces, cut a little square out of the big piece and secure it to the outflow with a rubber band/hairband without metal. Like so:
After your tank has established its cycle and all your levels are stable, you can go down to making 25-30% water changes once per week with a gravel vacuum, but until then you'll need to make several small partial changes to keep the ammonia from getting up to high. Callistra posted some great links on the previous page, I suggest reading those over and probably looking into picking up a a liquid test kit(not the strips, those tend to be quite inaccurate)to monitor your levels.