Maybe s/he does still work for the employer?  With that amount of work I would certainly expect to get paid!  But if it adds to your workload, it would stand to reason that said company would also be paying you.....

I haven't had this with a boss, I have had it with coworkers.  We were a new startup company and a similar company had just closed down operations so we had 7 staff hired in from old company (large percentage in a staff of 30).  To this day, 2.5 years later, I still hear "well when we were at such-n-such company, we always did things this way".  It has been a constant battle to get them to let go of the past and bring them around to a new way of doing things.  Very different from your situation, of course, but I can see your struggle with past "ghosts" and trying to get boss to cut the cord.

My advice would depend on the relationship you have with boss.  Are you comfortable having a sit-down meeting with him/her and just putting it on the table: "I appreciate the confidence you have in me in handling all aspects of your workday; however, the demands put on me by your continuing duties from your old position are not feasible given the demands of our current employer.  I will need to step away from anything to do with old company in order to focus on my current workload."