https://warlight.uservoice.com/forums/77051-warlight-features/suggestions/9148579--clan-tab-in-the-select-players-and-add-or-rem

I have all of my clanmates as Friends (except Cata lel), so all I have to do is type "coali" into the "Friends" tab, and then everybody from my clan pops up. It's not too hard ;P

Thank you for that great hint! (seriously)
However, this does not really solve he problem for poeople who dn't want to add houndreds of players to their FL only becausetheir clan is too big.