There is a simple way to do this in Multiplayer if you have the Asari Adept character. She's fully biotic and has an ability called Annihilation (
+
) that deals damage over time and primes all enemies in it's field.
Her other two abilities, Lance and Throw are both detonators. So it's as simple as activating Annihilation, getting close enough while it's active, and then using Lance and/or Throw to Detonate.
Annihilation is also available under Biotics in Campaign and does the exact same thing. So if you can't unlock the Asari Adept in MP, Spec into Annihilation in Single Player.