I setup a home theater for someone several years ago and had to use a wireless HDMI setup to the projector since there was no way to get into the ceiling.
Used a setup from DVDO that worked quite well. Even would transmit 3D just fine. Little slow to sync, but very stable. It was an early version of their "air" product line that was only good for in room connections. Looking at their site today it looks like they are only still good for in room transmissions, up to 30 feet.
Another option is to go HDMI to Coax. Never used one, but might be worth a shot. If you have to attach two "F" connectors to get to the outside TV, make sure to use a jumper rated at 3ghz or higher.
HDMI to Coax