Just realized that I read your note wrong, and that you were trying to split a 0.75 mg pill to get to 0.5 mg.  If you had to choose only one strength of pill, it might still be easiest to work with only the 0.25 mg pill....you could just take two of them to get to 0.5 mg, and not have to do any pill splitting, at all.   Just a thought...