Yeah, I'm very bad with that too. Been walking around like a shrimp for decades. I started doing pilates the strengthen my core muscles and when I'm driving, I try to keep my shoulders in contact with the back of the seat. I drive a lot, so I get a lot of benefit from that one. I know what you're saying about the not being able to force it thing. You're dealing with a long time of contracted "front" muscles and over stretched back muscles. It's going to take some muscle retraining to work that out.
You just have to see your distance...you don't have to like it.