adding a undo button to Spline Drawing Tool (spltool)

Has anyone here ever used the spline drawing tool in file exchange?

http://berkeley.intel-research.net/arahimi/splines/html/

I've tried something like this, I found online,

http://people.csail.mit.edu/jskelly/blog/?x=entry:entry090502-092926 but it deletes all the points at once.

function undo_plot(h, n)
% UNDO_PLOT Undo last 'n' plotting operations.
  
if nargin == 1 
  n = 1;
end
  
if n < 1
  error('Can''t undo < 1 plotting operation!');
end
  
figure(h);
children = get(gca, 'children');
  
for i = 1 : n
  delete(children(i));
end