Just thought I'd post this, as it worked out so well I think others might like it.
I had to drill new holes in the stereo mounts to drop the D3 further into the dash, then I gutted the factory head unit, flattened the back side, and it slips in as a dummy cover over the D3. Small pull tab on the left makes it easy to pop out on the fly, but all of the important info (Ipod info, XM, even nav data) shows though the factory cover.
And even looking close you can't tell it's anything more than the factory stereo.
note - the volume button just sits on top of the D3s volume dial. It is not attached, but deep enough that it stays in place. I forgot to pull it off for the open pic.