I know it's a bit early but one thing you guys can do is nominate "Sam & Max 2" for the 2004 Vaporware awards at Wired magazine. Wired magazine has a list every year of programs, hardware & the such that were announced or were intended to come out but never did. I have not seen this option yet displayed on these boards, so I thought that I would recommend it.
Hopefully, LucasArts reverses it's decision & proceeds with making "Sam & Max 2." However, if it doesn't, perhaps you can "shame" them by placing "Sam & Max 2" high on the list.
Last year, there was a campaign to place "Fallout 3" (aka "Van Buren") on that list. While "Fallout 3" is still very far from a reality (Interplay has been in very serious financial trouble for awhile), Interplay has since reversed itself & says that they are looking into options of getting the game made. Was placing "Fallout 3" on the list a factor in that reversal? I don't know. However, it didn't hurt.
Anyway, I hope that LucasArts is convinced to reverse their decision & make Sam & Max 2.