I bet you can do this by Right-clicking with the hammer instead of left-clicking! But it will take two energy, and therefore require the first energy upgrade AND the hammer before it can be unlocked. The boom effect is similar to Spider-tron's bombs until you can find a better AOE attack mechanic. And you're immune from your own particles, much like Spider-tron is immune to its own bombs (but not someone else's!)
And, as an added difficulty to an already pretty dificult enemy, Mk.3 Hammer bots have this ability as well.