Unless you ALREADY have a burning desire to do a thesis on a specific problem, you're not going to want to do a PhD in CS (especially if that's what you do now). When you're in mid-career, programs in the same field will want you to have a specific vision for what you want to do with your thesis. If you're pursuing a PhD because you're not super happy with the type of problem you're working on now, but don't have a clear plan for how to change direction, I'd recommend checking out CS-related fields, go to a few conferences (academics tend to be very friendly to this type of inquiry) and read a few papers, then pick an area that catches your interest. You need a compelling story in your application about why you're going back to school (I thought it would guarantee me a job at MSR doesn't cut it). If you get interested in a specific program, send them (either the program, or a specific professor whose work you're interested in) an email asking what to do about the letters of rec etc.. They'll let you know a) if you have a realistic shot at getting in and b) tell you exactly what they're going to want to see. This isn't undergrad admissions, there are few hard and fast rules about the application. If you get a professor who has funding interested in you, you're going to get a slot, period.
I'd check out Biomedical engineering, Computational neuroscience, Complex systems-type programs, Bioinformatics, Machine learning (may well be in the CS dept), and Robotics, to name a few. Programs like the above tend to have excellent private-sector placement rates, since a lot of people stay in academia and you come out with a slew of rare and useful skills.
Another thing to keep in mind, is that a PhD these days is a 5-8 year commitment (unless you already have you're thesis research mapped out, see above, then 4). While you won't be paying (in any reputable program), you'll only be making ~25k a year stipend. It's not something you should embark on without doing your homework about programs, and finding something exciting enough to sustain you through years of slow, slow progress. There were three mid-career people at my PhD program, and they were fun to have around.. but one thing that stuck out about all of them, is they came in having a research project they were already obsessed with, and they hit the ground running, where all the out-of-college types like myself spent a year or two testing the waters to figure out what we wanted to do.