We visited DLR last summer for the first time when Fantasmic! was closed. My 12yo son and I will be back for three days just after Christmas and I would like to make sure we are able to see it.
I realize that the CL is 9 all week and it will be extremely crowded. I considered doing one of the dining packages but my 12yo “adult” has a really limited diet and the only option would be Blue Bayou where he would be eating a lunch of plain pasta for $59.
How is the FastPass option?
We don’t have a ton of time in the parks so I’m hoping to come up with a strategy that doesn’t include staking out a spot 2-3 hours before showtime.
Most likely they will have 2 shows during that time and I would recommend getting a fp for the second show. I have heard it is not nearly as crowded as the 1st and it impossible to stake it out hours in advance, because the other show is going on. Also most that are at the first show, stay put until fireworks are over. So if you head over after the fireworks you will be on a level playing field.
Another (cheaper) option than BB is to do the hungry bear dining package. Not sure what your sons dietary restrictions are, but you could call and see what your options would be. We went to BB in early Jan and they worked with my son (also 12). No dietary restrictions, just picky. He ended up getting an adult portion of the kids Mac n cheese.
That sounds doable.
Mine is picky and on the spectrum. Unfortunately, mac & cheese isn’t on the list of foods he will eat. I did check out the Hungry Bear options…nothing on their menu works. 
I would still call. My sister is a vegetarian and one of the Disney restaurants we went to didn’t have any veg options she liked. The chef came out and asked what she wanted and he would make it for her. They came up with a sort of stir fry and she loved it! That is one of the reasons we love Disney! They are very accommodating. Since he is on the spectrum you could also talk to guest services about possible seating options at f!