ok let's try that again?!?!?
I have a rubber lipped pleco too, and he never seems to eat, I have tried cucumber, algae wafers, zuccini, romaine & iceburg lettuce, the insides of thawed frozen peas....you name it i've tried it, but I have had him for 3 months, never seen him eat yet, but he's happy & healthy and always sucking the glass at night...I wouldn't worry too much, as long as he's healthy and active, he may just be eating at night when the lights are out. Try the insides of peas (just take off the shells and smoosh it up a bit before you put them in the tank) put it in right before you go to bed, or around the time the lights go out...you may find they have "magically disappeared" in the morning, I only give him about 3-4 (cuz then my catfish get piggy and eat it all before my pleco does).
Good luck!!