
I can't add much to the good advice you've had already, only to agree with Teri and say please, do not force him to do anything he doesn't want to - even if he is happy once he's where you want to go. It will make his fear worse in that difficult spot.
Try encouraging him to move with treats or a toy, whatever he loves - if he really won't do it, then get in the car and drive. And remember to be patient - it'll take a while to get him past it, I doubt he'll get over it on the first walk!
Think of it like someone forcing you to face something you're frightened of - spiders, say, or clowns - would you feel better about them if you where forced to confront them or would it increase your anxiety? I have mild social anxiety - I won't even go into the canteen at work if it's full if I can avoid it at all (it's a VERY small canteen, more like a big front room), and every time I've had to hasn't helped in the slightest. Except to make me quicker at getting what I need - I'd be worried that your lab might go a similar route, increasing his reactions until he finds something that works and stops that situation.