Considering Plaguebearer's ability can't target black creatures, I'm pretty sure there is indeed no possible way.
If that wasn't a factor, though (say the Plaguebearer was Purelaced), I believe it's still impossible, unless you were the active player. Non-active player gets the last word in infinitely repeatable actions, so if he were non-active and you were active, he could get the Elemental's ability to resolve and then have a chance to use its new ability.
I believe he was the active player (having just cast the elemental) - although as you pointed out, we all blanked out on the non-black creature clause, so it should have been moot.
Going up 3-1-0 is not the hotness
Not if you're playing more than 4 games. I think you had the best deck, but we ended the night at 3-2-2, since Triple_S and I quickly learned to try and keep you in check.