I’m about at my wits end, and don’t know where else to turn. My dear lazyweb, please come to my aid before I start crying.

I have a toplevel window. I wish to remove decorations, place it at a specific point on the screen, and give it a specific size. This arrangement is so I can have a single window covering multiple monitors in a xinerama configuration. This doesn’t seem like it should be so hard.
Doing this over a single monitor seems to work just fine, at least with metacity. My window happily goes “fullscreen”, covering the panel at the top, on the monitor I expect it to. Then, when trying to move_resize it to cover both of my heads, things get bad. Attempting to set it to 3200×1200+0+0 gives me a window which is 2721×1200+1600+0 (the minimum width as per gtk size request, correct height, bad X and correct Y). Note that this is transitioning from one screen to both.
Kwin does a little better. Depending on which head I attempt, it may go “fullscreen” on the wrong one initially, but it seems to work after that.

Setting this window as override-redirect causes all sorts of more-bogus behavior, so I’ve pretty much given up on that. Getting a new hint into EWMH for multi-head-fullscreen-windows is the correct thing to do, but I don’t have nearly enough time for that right now, and this has to work with current (and older…) window manager releases.

Help?