I recall that this sort of thing has been said in the forum to be difficult if not impossible. This discussion might help. However... that Java editor seems to have a non-standard, indeed gimmicky, input method there!
So the character is typed as normal, and then the text cursor is positioned in front of it? Just typing the character and using the left arrow key would surely be quicker, more logical, conventional and convenient! 
Have I misunderstood?
If the editor is actually offering a feature that is more useful than how I understand your description of it: might there be an alternative (and easier to automate) way of accessing the feature, e.g. through the application's menus?