If you can't elongate the holes enough, there is something wrong with suspension parts being bent or the frame. I've gotten 3 degrees of negative camber out before this way, and still had some room left to elongate... If you ran out with CC Plates, I'm sure you could actually elongate the holes and move it over, then adjust with the CC plates if it was THAT far out.
My opinion
The places that have a hard time getting a good alignment out of stock plates are the ones who do not elongate the holes. I would worry about the loss of material causing fatigue strength issues. How much edge margin do you feel is acceptable? Also, the vast majority of aftermarket CC plates are quite thick, which implies increased rigidity for a part of the vehicle which sees some decent loads, I feel this to be pretty important. Finally, I have found it challenging to get a decent alignment done. Sometimes it is because the alignment tech is a rookie, and other times he just doesn't know/care what he's doing. Either way I don't want to put an extra burden on a guy who is already having a hard time with parts of my car that my life depend on.
More than I planned to write here, but its fun to get up on the soap box.
Oh, Yeah. I installed the BBK (I think they were BBK) CC plates a few years ago. They went in easily and look pretty decent. No complaints from the alignment shops.