I am not sure if this would work for your filter, but on a large tank I had in the past there was an inhabitant that made rather large droppings as well.
What I did was took the griill off and modified the bottom a little bit.
I am going to try and illistrate it here, I don't have the tank anymore so I can't show pictures.
( if it doesn't show right on your screen, copy & paste it into notepad on your computer and set it to a fixed width font like Courier New or Fixed Sys )
Normal Filter Grid Looked Something Like This: Yeah it isn't pretty but you'll get the point.
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I took my dremel tool and widened all of the holes. In the end It looked like this:
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I staggered the holes thinking that if a piece of dropping blocked a hole the force from the adjacent hole would help to rip it apart. Just take care to make sure you don't leave any sharp points. If your grill is plastic, you can heat up the end of a safe wire and melt the sharp point down a little bit.
Anyway, just thought I would post it so that maybe you could just modify the filter and save you a couple bucks.