I've run speaker cables along the corner where the baseboard meets the carpet. I used a screwdriver to jam the wire as far as it could go. Most of the time the wire can be nudged into the available space.

Alternatively, you could pry off your baseboards, staple the wire to the underlying wall as tight to the ground as possible, re-mount the baseboard right above it, and nail in in shoe-rail or quarter-round so nobody can tell the difference.