Want to get any of the Fantastic Four from SoD in BG2EE? Or maybe all of them?
1) Tweet about them, what you like about them, and how much you'd like to see more of them. Hashtag #Dragonspear
, probably more effective to direct tweets to Wizards of the Coast than Beamdog, but both would be best.
2) Seek out Beamdog and WotC folk at conventions/shows and tell them face to face that you'd like to see them return.
3) Cosplay the characters, let people know who they are and where they come from, and especially make sure people from WotC and/or Beamdog get to see them, ideally in person but at least in pics. That's a big ask, I know, but I also know a few different people showing up to a con as Glint or M'Khiin would probably make a bigger impact than anything else.
4) Create fanart and post it everywhere you canSource
Also, there's a forum poll
about this subject.