I was recently in a similar situation. Although my time away from academia was somewhat shorter than yours (10-15 years), and even though some of my professors were still active in research, I did not think they would be in a position to write a strong recommendation letter. "I vaguely remember this student from 15 years ago, and she got A, so she must have done alright," is not the sort of recommendation you want.
My solution, which has worked out well for me, was to spend a year taking graduate level courses at a local university. In addition to taking the classes, I went out of my way to introduce myself to the professors at the outset and explain my situation. I was able to get involved (in rather minor roles) in two research projects, one each semester. This allowed the professors to write much stronger letters than I could have gotten from professors of 15 years ago. It also had the benefit of improving my applications with recent, relevant coursework and research. Even if you have all of the requirements, some recent academic experiences may be valuable, depending on your field. "Fulfilling all the requirements" and having a strong application are not quite the same thing.
Of course, this may not be applicable to you. It is a full year, at least, without funding. It requires a nearby university at which you can get involved with classes and research. It delays your starting time by at least another year. These are all drawbacks, and may be more or less burdensome depending on your situation.