I just think that Edward would never ever have done such a thing... It would have been improper... Look at the rather shocked view that E takes about Willoughby asking Marianne for a lock of hair.. and at least that is done openly between a couple whom she beleives are at least openly "attached" if not engaged....

I think that JA just couldn't think of any other way to introduce the "hint" that Edward has another woman... and so she had to "make" Edward wear a ring with Lucy's hair (which I dont think he would have done) and then she "made" Elinor on thinking that it was her own hair, forgive him for it.. which I dont think Elinor would have done...