I am turning this round and looking at it from the other side though - how bloody rude is this guy?!
It's fine to want to make plans to see your friend/sister/ whoever that you don't often get to catch up with, alone.
It's absolutely not fine to ask anyone to facilitate the trip in this way.
It would just about be ok to say, would you be amazing and give me a lift there, then I'll get a train back/stay over. (Or rather, if sis wants him to go to her so she doesn't have to move a muscle - perhaps she sorts it? hey bro, know it's awkward getting all the way out here, how about you stay over/I pay a taxi to nearest train station?)
But to actually say, can you take me all the way there, then sit in the car out of our way until we've finished, then bring me back?
I'd be so insulted by that and gutted that my partner could be so rude and entitled. It wouldn't really be about not being invited. It would be the whole arrogant rude package. I'd refuse because I'd feel I was being made a right fool of, and I'll go out of my way for anyone.
I would raise all my eyebrows at once and suggest politely that perhaps they meet in a mutually ok location. Or he stays over. I might be able to give him a lift there, if he plans to stay. Otherwise - no, I'm your partner, not some kind of employee. Give your sis my best...