I'm not too fond of the idea. I would think that they would cloud your water. Your fish won't die if they go 4 days without food. I think it would be a better idea to invest in an automatic mechanical feeder.
they also eat alot of things that grow in the tank, and i have noticed with many that after a day of fasting they'll be digging around in the gravel for any uneaten food, so don't worry they'll be allright, 4 days isn't long at all.