Labour could promise another referendum, make it binding, for some future date. Big risk, because they could vote to leave, but then the SNP threaten to sort a new referendum out all the time anyway. It could negate a lot of the SNP vote.
Another huge thing we could do is move the capital north. It seems crazy, but countries have done it before. Brazil built one from scratch. Westminster seems very remote to parts of the country, both in distance and in terms of its interests. Manchester comes up frequently when people navel-gaze on the issue, but I genuinely think Liverpool is a better fit if we want to maintain links with the Irish.
We English can be some right fuckers in our treatment of people from other parts of the Union, and I've never understood it. I have been to every part of this union, and to the Republic of Ireland too, which no longer is part of the Union, but very much influenced by it. Apart from a few things dividing along sectarian lines, there's no difference bar the accent and sense of identity.
If we want to hold this union together, we go a funny way about it sometimes. Respect goes a long way.