Perhaps, if the OP does not already have one, a Master's Program is a good way to start? Is does not require a dissertation and many have a non-thesis option if you do not want to do original research.
Of course, you do need a fair degree of motivation to finish even a masters, but it is a much lower bar than a PHD. While your direct advisor may or may not pay you much attention, most masters programs are centered around a series of classes that are like a harder extension of your undergrad education.
Also, if you are doing this for career purposes, a masters is a "sweet spot" in terms of return on investment in education. It is much less costly than a PHD, and does not run the risk of intimidating potential employeers in the way that a PHD might. But at the same time, it sets you apart from people holding only a bachelors.
(For full disclosure: I am currently in a masters of math program while working full time.)