Here's another sequential style mirror turn signal housing for your Subaru. Just swap these out for added functionality. This model also includes a DRL function for normal operation when the turn signals are not in use.
You can wire the DRLs using an add a fuse (in related products below) to the 12v plug in the interior fuse box. This will allow the DRLs to turn on when there is accessory power being supplied to the vehicle.