Anticipating the same problem we had with the original Cattle Feeder/Rice Dispense (namely, rice) I've decided to pre-empt as many blockages as I can with... some paper!
With rice being as annoying as it is, the less ridges, cuts and tape used, the less rice will get snagged on its journey to the spout. The less rice that gets snagged, the less chance of blockages ruining our day.
This may look like random shapes to you, but what you're looking at is a single sheet of A3 cut and folded to polygonal perfection. When folded, this slips inside the rice dispenser, covering all the lego holes and sending the rice to a near-friction-free journey to the troughs.
I know what you're probably thinking... "Can we see a photo of it in place?" No you can't, because I didn't take one. But you'll have your chance.