Well, this is a little sneaky, but you can try this if you absolutely need to have this functionality. First, you can find the menu item with the "Plot Edit Toolbar" label and look at it's Callback property:
f = figure;
M = findall(f, 'Label', '&Plot Edit Toolbar');
Now that you know what it's doing, you can call the same function that its using in your GUI.
I think we're getting into somewhat "undocumented" functionality here, so the standard warning about that (functionality could change in a future release without warning, etc.) applies here.