We went on a 3 day package tour to the Sunderbans with Bengal Tours (
http://www.bengaltours.com/flash/sundarban.html) last December. There are 2 other another similar ones, but cant recall their names.
Your friend can get in touch with them to see if they can arrange something of this kind (there were involved with a natgeo team as well, and several other Japanese, Dutch documentary expedition teams). Mind you, the tourist season should be off by now, basically they dont operate any of these tours in summer cuz of the heat.