Many times, if you pull the baseboards you will find gaps to simple push the cable into. As Elizabeth suggested a router will make it easy. You are working on the back sides of the baseboards any way.
1 piece of advice: After removing the baseboards, pull the nails all the way through instead of pushing them out and splitting the wood. Then, just buy new finish nails.
1 piece of advice: After removing the baseboards, pull the nails all the way through instead of pushing them out and splitting the wood. Then, just buy new finish nails.