Make vague obviously inaccurate promises ("real soon now" or "shouldn't last much longer" is a good one, especially when it's been a significant period of time since the last update.)
Remove the user's ability to reply.
grrf. geez, LJ, get a PR department! would it really be hard to set up a script that lets you type in a one-sentence description of what you're doing, and a timer to remind you every half hour or so when the servers are down?
And disabling comments on the lj_maintenance post is just counterproductive >_