I agree that would be great, but I don't know if it's possible. The current clients are basically doing password cracking/hashing - that probably wasn't one of the "good causes" you had in mind. 
The miners are not trying to crack anyone's passwords. The proof-of-work system defends the blockchain from brute force attacks. If you can actually think of a better way to do it, speak up; but many minds have been bent to this problem in the past.