How to draw only left and bottom borders of the frame around a plot?

Have you had a look at what SAGE did with mpl? Their

    > axes are Mathematica-like, and their API exposes the
    > geometric primitives in Mathematica's plotting API. For
    > example:


    > That plot is actually done with MPL.

I know what they did, and it is basically a hack so it is not suitable
for the core. Basically, they just turn off our axes and rewrite
their own with lines ticks and labels. We can do something similar
(and need to) but we'll need something more flexible that is built in
rather than tacked on. Just a matter of finding the time...