I remember that Dave Grohl once celebrated his b-day on a show too. They brought on a huge pink box on stage and LO! the Scantily Clad Girl de rigueur comes out. Dave looked extremely embarrassed and went kind of right on with the show.
I was thinking what could jump out of a box onstage for Stewart...
Maybe it depends on who puts the present in
1. A hand grenade (Sting)
2. Mala beads (Andy)
3. Big Paycheck (tour manager)
4. A message "Honey, guess what?...We're expecting!" (Fiona)