I've never seen anyone do them either, but I've got a couple guesses.
Could try tanking them with a heavlly buffed pet. Pets generally can't be banished and i did 2 of the 4 praesertums in Sanctus Seru this way.
Another thought...you could just kill them all at once. You'd still only have to tank one at a time, so slow, banish, slow, banish, slow, banish....then
dot, banish, dot, banish, dot, banish
repeat until dead. they should all three drop dead at about the same time