"..If you drop the sunroof drip pan from below, you still can't remove the sliding headliner panel. It won't slide out the back of the mechanism without surgery..."

On the one and only headliner I did, I removed the inner sunroof panel via the dropped rear end of the pan. I found this method to be fairly simple and I didn't have to go through a sunroof re-alignment process when putting it back together. The trickiest part is separating the inner sunroof panel from the sunroof itself. First you'll need to disconnect the springs under the rear edge of the sunroof with the sunroof open in the "vent" position - I believe this is detailed in the 700/900 FAQ's. Then close the sunroof down flat. To separate the inner panel.... As i recall it requires significant upward pressure on the inner panel combined with an authoritative yank backward. Once the two pieces are separated, you can unscrew the pan all except a couple of screws along the front edge to keep the pan aligned with the roof. To support the rear end of the pan so that it doesn't drop down too much, loop a length of rope or cord under the pan, out both rear doors, and tie it together over the roof of the car. This will allow the rear of the pan to drop about 5 inches - not enough to cause serious bending along the front edge which is still screwed to the roof. Then slide the inner sunroof panel to the rear of the pan. When it hits the rear of the pan, reach in over the rear of the pan and lift the inner sunroof panel up over the edge of the pan. The tracks in the pan that the sunroof slides back in, have openings in the last couple inches to allow this.

Some worthwhile reading:

http://www.brickboard.com/FAQ/700-900/InteriorTrimandPanels.htm#HeadlinerDIY

Good luck!