The scrolling workaround in that page is just these two lines of code:

var scrollTop = txtarea.scrollTop; /* change text and set new selection here */ txtarea.scrollTop = scrollTop;

The rest of the JavaScript code on that test page corresponds to code you'd have anyway - replacing the selected text, setting the new selection, etc. You don't need to replace your existing code to implement the workaround, just save and restore scrollTop at the right place.