how long are you going away for? I have never used a pyramid feeder before, so I couldn't comment on how well they work. I think I really meant for small fish, not big fish like Oscars and plecos, I think you'll find that it won't last, you may also find that the Pleco will just eat the whole thing before it has a chance to dissolve, after all, they have got quite powerful mouths.
There are a few automatic feeders that you can put pellets in,, but again, I'd never used them myself so I can't give you the benefit of any experience.
www.aquariumguys.com/pyramid7day.html
www.aquariumguys.com/aufe.html