As with all Toyotas, Homelink is always on. No key needed.

This is a very simple fix, described in other forums.

First, I removed the black plastic trim adjacent to the headliner. It just
pulls off, then slides out from under the headliner.

Then I unplugged the mirror. To give myself more room, I removed the mirror.
Just 1 Torx screw, then it slides upward from the mount.

The plug has 3 wires. Red is hot, blue is switched on with the vehicle,
white/black stripe is the ground. I stripped away some of the housing to give
myself more room to work.

Just cut the red wire and connect the plug end to the blue wire. This will give
switched power to the Homelink buttons. I did this by stripping the wire with a
utility knife and soldering. Then just some electrical tape to isolate the
wires.

The Homelink memory is retained even though it loses power when the vehicle is
off.

source: http://www.myrav4ev.com/forum/viewtopic.php?f=9&t=928