You just need a Waver of your own, then choose one of your friends who has one as well. Then, once one of the Wavers has used his skills, swap him with Atalanta for buff and gg.  

It takes a specialized setup of servants not everyone is going to have, which is why most people probably wouldn't pick the CE.  

Luckily, I have them.  

e: Also, pretty sure the turn-based CEs aren't ticking when you have them on a backline unit. You could also sit Scath on your backline and call her in when needed on the final wave. So yeah, it's not as bad as people think.