I understand the danger of flying the magenta line on approach since that hasn’t been surveyed and can lead to CFIT. However, when given enroute vector like this, you presumably would be above the MVA. So the routing is for ATC to separate you from someone or some airspace. Given that, how accurate would you need to be to get on course and simply set a heading until you could get the box programmed? I would think 3nm either side of an expected routing would be adequate and could be hand flown with a heading off or foreflight or similar until you had time to set up the box correctly? I know this isn’t considered correct but this kind of situation isn’t flying a surveyed route anyway.