I also work full time and go to school almost full time in the evening, so I know how it is.
First off, let's be clear on this: what GPA you get for not studying depends on various factors, including your school's grading standards, how smart you are, what material you've covered before (either formally or informally), what major you're working toward, and of course how must work you did relative to how much work your classmates actually did.
There is no free lunch. There is no easy way out.
I study, I keep up on my reading, the program I'm in is competitive, and as I sit here at the halfway point for my degree the lowest grade I've gotten (earned?) so far is a B+.
One thing I can tell you is that I'm tired all the time. I'm also way more cranky than I ever was before this began. So, umm, two things.