The following works as you requested. You can of course modify the code in more elegant way with numbering handles as ax(n) etc . Also, I slightly cheated with the size of axes to hide boxes and tick labels of smaller axes behind.
hFig = figure();
% p0 = plot([0,1], [1, 2], 'r');
% ax0 = gca;
% pos0 = ax0.Position; % the default position is [0.13, 0.11, 0.775, 0.815]
%
% make the position slightly bigger than the default one to overlap the tick
% labels from smaller plots
pos0=[0.09, 0.1, 0.85, 0.85];
ax1 = subplot(2, 2, 1);
pos1=ax1.Position;
p1 = plot(ax1, [0,1], [1, 1], 'b');
ax2 = subplot(2, 2, 4);
pos2=ax2.Position;
p2 = plot(ax2, [0,1], [1, 2], 'r');
set(ax1, 'ButtonDownFcn',{@subplotZoom, ax1, pos1, pos0})
set(ax2, 'ButtonDownFcn',{@subplotZoom, ax2, pos2, pos0})
function subplotZoom(~,~, ax, pos, pos0)
if get(ax,'Position')==pos0
ax.Position=pos;
else
ax.Position=pos0;
axes(ax) % bring axes to the focus
end
end
