I don't know of a way to do that by setting legend properties, but you can create "dummy" lines that don't appear in you plot but do hold space in the legend.
Here's an example of plotting 16 lines in a loop and after the 5th and 10th lines are plotted creating the "dummy" lines for the legend:
hold on
for ii = 1:16
plot(1:10,rand(1,10));
if ii == 5 || ii == 10
plot(NaN,NaN,'LineStyle','none','DisplayName','')
end
end
legend('NumColumns',3)
I imagine that you should be able to do the same in your code by inserting plot(NaN,NaN,'LineStyle','none','DisplayName','') in the right two places.
