After thinking about it, I think the way I'd do it is this:
EF = Sanguine
ET = Choleric
IN = Melancholic
IS = Phlegmatic
Maybe ESFP can be the pure sanguine, ENTJ the pure choleric, INTP the pure melancholic, and ISFJ the pure phlegmatic. That would allow for the secondary temperaments - for example, I'm INFP, so I'm a melancholic blend because of the IN, but the remaining two letters are FP (together in the pure sanguine) so that would make me melancholic-sanguine (which I do think is the blend that fits me best).
It might not be perfect, but I think it works pretty well.