AFAIK OpenSSL has hooks that can be called when a certificate needs to be validated. If I my memory is correct this could be used to validate certificates using a public API (basically doing the same as Apple's patch, but using public APIs for the system and OpenSSL).

This has one significant risk though: as we've found at a couple of times (such as with the _scproxy extension) Apple's API don't necessary play along nicely when you use execv without fork or fork without execv :-(. I have no idea if Apple's preferred crypto APIs suffer from this problem.