Why can't the British compromise and choose not to enforce the border at all? Act as if Northern Ireland was still part of the EU? The British can still have their precious border only it'll be somewhere out in the sea between Northern Ireland and the mainland of the UK. Or, perhaps better still on the mainland.
After all, like Scotland, Northern Ireland voted by a significant majority not to leave Europe, because Europe is so beneficial for them, to do otherwise would have been nuts. Respect the democratic result in Northern Ireland if one is so attached to democratic ideals and respects the interests of the people there.
Only this would kind of signal that Northern Ireland was 'different' from the rest of the UK. Surprise, surprise, if one has been there, it's pretty obvious that it is rather different.
I think this would be a reasonable compromise, say that the border exists, but in reality, ignore it and create a new one somewhere else.