I think that the zorder
keyword argument should help you:
julia> using PyPlot
julia> xx = linspace(0, 2pi)
0.0:0.1282282715750936:6.283185307179586
julia> plot([0, 2], "b", zorder=1)
1-element Array{PyCall.PyObject,1}:
PyObject <matplotlib.lines.Line2D object at 0x129216b10>
julia> fill(sin.(xx), cos.(xx), "k", zorder=2)
1-element Array{PyCall.PyObject,1}:
PyObject <matplotlib.patches.Polygon object at 0x1293a7f10>