Pleco help- on his back?

[Moogled]

Just place him in the garbage bin.

Sure it might seem "mean" as you say, but it'll be over before you know it. Unless this fish has extreme sentimental value to you, it's probably not worth going through all the trouble of digging a site and burying him.

Besides, your other option was to flush him down the toilet anyways. Just that he didn't fit, right?