I have customized the iOS implementation of CCEditBox in my project to solve the issue #1971 and some other problems. It already supports placeholder customization partially.
The customization I made is that UITextField is visible only when the CCEditBox is in edit mode. And in non-edit mode, UITextField is hidden and CCLabelTTF is shown instead with all same attributes at the same place. So the placeholder in non-edit mode can be customized.
I think that this customization is just a work-around for some problems and definitely not a perfect solution.
But it is still useful, so I'm going to issue another pull request for this after current pull request.