Leave your clan with all your alts so only your main is left.
Join with your alts as supporters.
???
Profit!
To make the actual clan size more appearant they made it so you can only have 1 dude in a clan, while any alts would have to be "supporters". You can't add any more alts before you remove the multiple characters that are currently "full members". After some weeks, a script will be used by the devs to take out any remaining multiple chars in the same clan (as non-supporters) so only 1 char remains as a full member.