If you have a large piece of driftwood in your tank which the pleco hides under you can use the "tube" method. A length of 1" diameter pvc pipe is all you need. But this really only works if the driftwood is big enough that the oscar can't move it, or fit underneath it where it can steal food.
You place the tube so the end is under the driftwood, it helps enormously here if your driftwood has a gap in the top. Then you drop sinking pellets down the tube and they nestle on the substrate where the pleco can eat in peace.
I used to try feeding at night but as long as food is out in the open other fish get wise. I also tried the "diversion" method but I found that my other fish got wise to that too. But if other fish can't physically get to the food then that's another story.
So, heavy driftwood with a gap in the top that your pleco can get under but your oscar cant, and a length of pvc pipe.