the only way i know how to throw chain lightning at different people is a hassel but i've done it...

i only have 2 shammys but i use my G15 and have 3 buttons set aside for this,

button 1: /assist <main> /setfocus (for 1 shammy)

button 2: same thing but for shammy 2

button 3: /cast [target=focus] chain lightning