First, with a wiring diagram, what I suggest below might change, due to if Toyota is offering a factory/Dealer option, the system may be pre-configured etc.......
Depending on how the LC is configured......
If it has "puddle lights" (lights that illuminate the ground around the doors when they are opened) you can locate the wires in the connectors behind the Dvr's/Passengers kick panels and tap into them, easy deal.
If it doesn't have puddle lights, you will need to find the door (dome light) trigger wire(s) and determine if it is a "always hot" circuit, waiting on the "ground" connection or a grounded system waiting on a hot input. Determine if the dome circuit is powered by a relay, if so you can tap into the circuit from the relay output.
The trigger wires should be accessible at the connectors located behind the Dvr's/Passengers kick panels.
If I were doing it (with puddle lights) I'd locate the light's wires behind the kick panels and "posi-tap" into them.
Without any type of additional lights when the door opens, I'd locate the trigger wires behind the kick panels and "posi-tap" into them and wire in a fused relay to power the sill lights.