To be honest I’m not sure that remaining in a customs union indefinitely would be sensible, but I’m all for the “Norway for now” approach.
It would never happen, but the way I would do it would be:
Initially a soft Norway style brexit
After a five year period hold a referendum at which no deal, rejoin, soft Norway brexit or bespoke Brexit (if one had been negotiated) were all possible options, using an alternative voting system. But with the proviso that if no option receives more than 60% of the vote in the final run off then we continue with the Norway option for another 5 years, at which point repeat the referendum.
If any option receives more than 60% of the vote then that becomes the “settled” outcome. A future government could change that, but would first have to win an election with their proposed change included in their manifesto, and would then have to win a referendum with a 60%+ margin