Re: who would be good canidates for adding the knuckleball?
Knuckleball is a pitch that requires such a feel that you really can't use it as a second or third pitch, you have to throw it almost every pitch. So you are talking about basically trashing everything you have in your arsenal, that you have worked years to develop, to add something that you have never used. For that reason, the only time you see a guy try it is when he has reached a point of total desperation, meaning he is on track to be released and likely not ever be picked up by anyone.
That being said, if a guy, likely a Single-A pitcher, has been told and has seen with his own eyes that he simply does not have the arm to ever compete at the big league level, he might try this if he shows on the side he can throw a pretty good one (most guys have messed around with trying to throw a knuckler at some point in their lives, just for fun, just like all of us probably did a few times). Most guys can't throw one. A few can throw it well enough to convince their organization to give them a shot. A few from that group actually have success in games.
Wakefield was not even a pitcher when he started trying to show the Pirates organization that he could throw a knuckleball. I saw the first game he pitched in the minors.
Someone like LeCure would not be a likely candidate. He is a long way from giving up on pitching in the big leagues and even if he did give up on that, he knows he can make a living in Triple-A for quite some time at the least. A more likely candidate would be someone who throws in the mid 80's without a good secondary pitch. That guy knows he has nothing to lose. And out of all the guys who fit that description, only a tiny percentage would ever be able to develop the pitch well enough to get big league hitters out.
Once every few years, you hear guys on a team talking about a teammate who can throw an amazing knuckleball (he will throw it when the players are warming up for BP at 3:00 in the afternoon). Often, that guy isn't even a pitcher.