As part of another (unsuccessful) project, I found the trunk release switch from a Focus will also release the liftgate on a TC. I bought a switch from a local salvage yard for $30. It is easy to install by removing the side panel and popping out the switch panel with plastic panel removal tools. The switch sends a signal over the LIN (low speed network) to control the lights, trunk release etc.. Apparently the trunk release LIN message also releases the liftgate (actually unlatches to door, not just unlock like the button on the key fob). The switch will not activate if the vehicle is in gear.
Not sure if this is useful, but I had the switch so I installed it. I think a 2012+ Focus switch will work.