I had one successfully for a long time like that, the poor thing must've been so hungry!!
I do this for my iguanas, and because of the variety of foods that plecos can eat, this is perfect.
I take fruits, veggis, and greens, and chop them up into little shreds (a grater or food processor works better than by hand) and I roll all of my ingrediants together into little balls, and stick them into the freezer. When I need them, I thaw them out, but for the plecos, I'm sure you could just toss 'em in frozen and they'll slowly fall apart, unless a baby piranha is attacking it... -_-* Whiplash doesn't like carrots, so I don't know why he bothers.....
ANYWAYS, if you want pellets or shrimp or something to get to your plecs, this would be an easy way to do it.