The easiest way is probably just to add a small offset to the ydata:
nx = 100;
ny = 50;
ysig = rand(nx,1);
x = 1:(nx+ny);
y = nan(nx+ny,ny);
for ii = 1:50
y(ii:(ii+nx-1),ii) = ysig;
end
dy = 1;
ystaggered = bsxfun(@plus, y, (0:ny-1)*dy)
figure('color','k');
axes('color', 'k', 'xcolor','w');
line(x, ystaggered);
figure('color', 'k');
[hl,ha] = plotses(x,y);
set(ha, 'xcolor', 'w', 'ycolor', 'k');
set(ha(2:end), 'visible', 'off');
