Maybe you just need to change your narrative focus. In the case of Exploits, it's sometimes better to assume that the cause of the effect is not the person initiating it.
This is counterintuitive, since many Powers in 4e are easily assumed to be grounded in the character. The character is considered the source of the effect. For Come and Get It, you flip that assumption. When the Fighter invokes the Exploit, you, the DM, come up with a reason why the monsters would decide to attack the fighter. It's not something the fighter actively does, like a taunt, but a change in the battlefield that the monsters initiate. The most obvious example would be for one of the monsters to say something like "This one is weak! Move in to finish him, my brothers!". If they're non-verbal monsters, then they just make the decision to attack the fighter for their own inscrutable reasons. It's nothing that the fighter does, per se, but a monster-based decision.
In other words, the Fighter's player uses the Exploit, but the in-game rationale is that the monsters choose that particular moment to make a terrible tactical decision to focus on the fighter. If the character was describing the battle after the fact, he might wonder aloud what made the monsters choose such a tactical blunder:
"Yeah, they had us on the ropes, but then one of them thought it would be a better idea to focus on me. Can't imagine what they saw, but battle's a tricky thing. Can't say they lived to regret it."