If it was me, I would absolutely talk pretty frankly with my sibling about my concerns. I think your brother is valuing the fun surprise element without really looking at whether it would be fun for anyone else. It's probably just a touch of cluelessness, and another perspective could help.
This is what I'd do w/ my husband's little brother. When he was younger, he just didn't get it. He didn't see how anything affected anybody but himself.
I considered it important to point certain facts out to him.
He wanted to leave my hometown right after my wedding, and skip the reception. He didn't drive; so I said to him, "So you want someone else, someone who is there to celebrate our wedding, like my brother or your dad, to leave the wedding, drive two hours to the airport and two hours back, which will mean that they will completely miss the entire celebration and time with their family. All so you can leave early because you think you'll be uncomfortable.
"I can't ask anybody to do that. I don't think you should ask anybody to do that. I don't think you realize exactly what you're asking.
"If you think you'll be uncomfortable, please don't feel you're required to attend the wedding."
Then there was the time that DH was driving him back to college at Christmas and a nor'easter was heading in, due to hit at 9pm. The highway to his college was the most winding road I've ever seen, w/ no shoulders and no lighting (Taconic for those of you who know it). And it was a 2 hour drive. (and, end of December, so early darkness)
DH and I decided they needed to leave at 5:30, so DH could be home safely. Brother balked at leaving, so I said, "there's a storm coming, and it's going to hit at 9pm. That's not a safe road in that kind of a storm." He said, "but it's only a 2 hour drive, we don't need to leave until 7." I blew up, and said, "That puts YOU safe in the dorm at 9pm, and MY HUSBAND driving on the Taconic through the worst of the storm. My husband's trip does not end when he drops you off--he doesn't magically dematerialize and reappear down here. He has to turn around and drive TWO HOURS HOME!" (yes, I was sort of loud then). "It's not all about you. Get ready to leave." And I walked off.
He got much better. He's not selfish and mean--but he was very self-focused. And he just didn't THINK. He saw only the thing that was in his head.
This is what I'd say.
I would call Bro up and lay it all out for him to think about...
So Mom and Dad are going to be driving X hours on <whatever day> solely to be able to see you at Christmas time. They feel sorry because you say you can't get off for Christmas. They will be driving in heavy holiday traffic. They will not be spending time prepping for Xmas, but they do this all because they want you to have family at Christmas. Now, you are going to turn around and come home with them? That is like saying "Fooled you! Made you come all the way out here for nothing! I lied to you again about not being able to come home!" At some point you will be the boy who cried wolf and they won't bother.
With the "tone" of "I'm offering you another way to look at your plans. More info for you."