I read somewhere that it takes three weeks to form a routine. I think you're right--trying to work out after work is really hard because you're either mentally/physically exhausted or you end up staying later than planned at the office. So maybe one way to go is to plan on three weeks of hell--suck it up each morning for three weeks, and maybe reward yourself at the end of it by treating yourself to something you've really wanted. Do you have a best friend you can lean on keep you on track until you make your goal?
For a bit, I hired a trainer to meet me at the gym in the mornings. And then I had a training partner for awhile who could only meet at 5:30 a.m. on weekdays. After a bit, it became a routine, and now I've been doing my morning workouts for over a decade. At a certain point, you just fee like shit when you don't work out.