@AC (There's a lot of AC comments here, wonder why?)
Just leave Scotland in the EU and put all trade through there
Ideally, Scotland, Wales and a united Ireland. (Latest Welsh polling shows strong Remain support now - the original referendum had a lot of stuff you Cameron behind the vote, and farmers who thought it would cut down on the paperwork! Which it will of course - no more payments, so no paperwork!)
Anyway, that wouldn't solve it. There would then be a hard border between the glorious kingdom of Little England and Wales/Scotland.
Face it, the vast majority of citizens of the disUK are going to get battered, unless they own a hedge-fund in Ireland or a German passport.