Have you considered a strap or chain wrench?
I have a tiny one, not sure what size but if I had to guess 4" would be close. It's old and I have no idea where it came from, have had it for years and got it used. But I use it a lot in tight situations where a pipe wrench is a life saver.

Just out of curiosity what would one be working on that he used a 4 inch wrench?
Trying to remove a steering rack out of a car that's been in a accident. I've needed the wrench more than once. Tomorrow the torch comes out I guess.
. . 
Maybe a really small knipex cobra will do aswell it has some amazing grip one handed too
I wanted to suggest that. They are very small and strong, and the head is small enough to fit in most places.
That will work! 42 bucks for shipping to canada? I'll have to pass and find another! Now I have the name tho. Thanks for posting.

Going to give that a shot today.
It looks more like a 6" wrench to me?![]()