Since Zorro asked about a blues harp, I at first assumed that it would be a wooden comb but, after reading the thread talking about plastic combs, I realized that Zorro had said, "blues harp" and not "Blues Harp", indicating that he/she was not necessarily talking about the Hohner Blues Harp which does have a wooden comb.
A plastic comb like the Super 20 or the Lee Oscar harps don't suffer from the soaking and I'd guess that you could try soaking as suggested above. I used to soak my wooden comb Marine Bands in the sixties to make the reeds easier to bend, but it did make the comb swell and I would have to cut the swoolen comb ends off with a utility knife. This made them very rough on my tongue. Modern harps don't seem to require soaking to bend notes, but you can no longer replace them for $2.50 like you could in 1965.