Here's the response from Excelsior regarding the possibility of assigning grades to CLEPs in the future:
I am sorry that we did not get back to you sooner about assigning letter grades to the CLEP exams. I spoke to someone at Test Administration and they said that it is unlikely that we will ever be able to go back to assigning letter grades to those CLEP exams that have gone Pass-Fail. The CLEP sponsoring organization made the decision to stop providing the full range of letter-grade equivalents in their technical information. Without that information, we have no basis for computing the appropriate score cuts.