For the Princess Weekend, my wife's sister came along to spectate and just rode the bus with us to get there. We also stayed at POP. For the 10k, we went all the way around to the start with her and watched corral A start, then my wife and I went back into F for our start. She was able to see us start the race and then made her way to the finish to see us there. Not applicable for Springtime Surprise, but for the half, she came with us on the bus, but then immediately got on the monorail to see us at Magic Kingdom, then back to the finish.
It will be too early to take any of the normal resort transportation like the Skyliner, so he would need to take the runDisney bus, but be careful of the time, which might depend on which corral you are starting from and also figuring out where to go might be a challenge. Since my wife and I had done a few Disney races, we were familiar with the layout and could guide her sister on where to go.
Looking at the info online:
https://www.rundisneyexpo.run/expo
In the info, the table says the buses from the resorts run from 3:00AM to 5:00AM, but if you look to the info on the right, for the 10-Miler, it's 3:00AM to
4:30AM.
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In the map, I marked in red the path he would take from the Resort Bus Drop Off, through security in front of EPCOT, then Spectator Viewing at the Finish, then keep going all the way around the corrals to the Start. That walk to the start is about a mile. Best bet may be for him to just find a spot near the finish. The final curve (I circled multiple times) may be a cool spot as he could see you coming and rounding that curve and it may not be as crowded there as the actual finish.
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This info is also on that website:
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