The only problem with S-e-a-n converting is that there are other S-e-a-ns besides Callahan.  I wrote about S-e-a-n Fisher, for instance, and it's calling him Deab Fisher.  I worry about overinclusiveness, but I'm not going to be too put out by it either way.  And, it is likely the case that most times we type S-e-a-n or D-e-a-n, we're talking about ol' Callahan.