If you look at the documentation for legend, there's a syntax where you can specify the handles to the graphics objects you want to create a legend for.
hPatch = patch([1 2.5 4 3 2], [2 1 2 3 3], [1 0.5 0.5]);
hold on;
hLines = plot(4*rand(5, 2));
% Create legend just for the lines
legend(hLines, 'Line 1', 'Line 2', 'Location', 'NortheastOutside');
