With a strange combination of GeSHi, CSS, and Wordpress plugins, I finally managed to get an LSL code pasting solution I’m happy with:

default
{
    state_entry()
    {
        llSay(0, "Hello, douchebag!");
    }

    touch_start(integer total)
    {
        llSay(0, "Quit fucking touching me.");
    }
}

UPDATE: Got the colors tweaked right down to the background color; should be exactly the same as the in-world LSL editor (thank you, Apple Digital Color Meter).

Also, updated the GeSHi lsl.php file so that clicking the various functions and what-nots lead you directly to the right entry on http://wiki.secondlife.com.

My big concern now is that the colors/fonts are so close it looks like a screenshot; hope people realize it’s not (and that they can cut and paste).