If you have the Grand Black War Mammoth, it has 2 seats in the back. But hey! You want more people to sit in it? Than read on.
What you need -
1 Person with the Grand War Black Mammoth (Drops from Vault of Archavon, rare)
3~ People trying to mount up
Steps -
1. Player with the mount start summoning it
2. Have 2-3 people right click spamming you really fast and not stopping
3. If you failed repeat steps 1-2, Keep trying.
If it worked than usually 2 people would be in 1 seat, thus bugging your mount and allowing more people to come ignoring the restriction, (up to total of 5)
Have fun
by Zoniao