WARNING: This page is about a different car, the 2006 Subaru Outback and 2006 Subaru Legacy. However, it is still accessible from the selected car via links, so may be relevant.
Clean the broken portion with alcohol or white gasoline.
Mask both side of wire with thin film.
Apply the conductive silver composition (DuPont No. 4817) to the broken portion.
Fig 1: Applying Conductive Silver Composition To Broken Portion