You can aim your spot meter anywhere, provided that you provide enough exposure to compensate the reading. One of the biggest mistakes people make when looking at exposure is the conclusion that "proper exposure" exists.
there is no such thing as proper exposure
Instead of looking at exposure as a matching game, lining up zeros and triangles, consider instead the metered tone on a scale, with each step represented by one stop.
Zone System - Wikipedia, the free encyclopedia
However, simply pointing your meter at the place where you want it to be "properly exposed" won't do the trick, unless your model is indian or hispanic, is green grass or a deep blue afternoon sky. Pointing the meter at a light subject will cause the subject to under expose, pointing it at a dark subject will cause it to over expose. But you can compensate for this by adjusting exposure accordingly.