No ... leaving them in the humidor will not soften up a hard cigar. They will absorb humidity and swell, and get even harder to draw.
Some cigars are just rolled tight like that ... ISOM's are notorious for that. That's better than being soft and mushy (like some Perdomo's) ...
Use a Draw Poker, a thin pointed rod of some sort, or a similar device to bore out the cigar to make it easier to smoke.
I'm afraid ther is not much more you can do, except maybe try the opposite of what you said ... and let it dry out a little!