Have your friends told their son yet about going to Disney & being there for his birthday? If not...then they could do an awesome surprise!
We took DS for his birthday. We had his family birthday party and told everyone we were taking him to Disney and asked for Disney gift cards & money instead of birthday gifts. We then wrapped up the largest box- it was as tall as DH! Inside I had a musical birthday themed Mickey mouse that I had bought from Disney.com & a t'shirt that said "I'm Going to
Disneyland". I also put helium balloons inside the box. So when DS opened it all the balloons popped out and the whole family yelled "surprise!". It was SO awesome to have everyone in on the surprise!
But I'm OT now...
I always try and plan a few special things for DS but since he's 7, I'm not sure if they would work for a 12 year old??
I like to make him a special invitation from Mickey to come visit him at his home in Toontown- I mail this before we leave. I will also ALWAYS mail DS a postcard from "Mickey & the Gang" on our last day in DL. He usually gets this about the time we arrive home.
I've been known to check into the hotel while DH & DS are waiting in the car, run up to the room & put some goodies from Mickey for DS on the bed and then run back down to the car & pretend I never did any of that. So this way DS will get a special surprise when we open the hotel room door. Maybe someone could do this only put a birthday cupcake & balloons in the room??
If we go to a character breakfast, I will also make him a special invitation. This year we are doing the Halloween Party and I've told DS about it but said that Mickey can only invite a certain # of people and that we probably won't be invited. I know, I know...I'm cruel!

However, we will surprise him with a special, last minute invitation...
If you or your friends have the Disney Visa credit card, there's a special meet & greet just for credit card members in DCA. We always go here because DS's friends want to meet with only him for just a minute. At least that's what I tell him...since it's not open to the general public, there's really only been 3 or 4 others waiting. DS thinks this event is JUST for him.

Maybe your friends could tell him that the characters wanted to wish him a special Happy Birthday.
I believe that one of the restaurants inside DL also does a special "celebrations" package. But I don't know about it...maybe someone could help?
You can also buy a celebration gift basket from Disney.com.
Have fun!!