Between level 1 and 5 there are 8 bard implement powers that either have no damage keyword, have the fire keyword or have the fear keyword, Stirring Song of Baator require hitting not damaging so even attacks that deal no damage are valid for this feat. You said it yourself building for flaming weapon as implement is going to be expensive in feats&wealth, doing it "just" to hand out 5thp to one ally, once x round, if you hit doesnt seem particularly convenient, i'd suggest to drop the idea of the flaming weapon and simply chose 2 or 3 of these powers (maybe an at-will, an encounter and a daily) .
But i admit that my resistance is because i'd rater limit houserules, i agree with you, the flaming weapon errata is strange and i dont understand the reason, so yes, lets pretend this specific bit of errata never happened.