I don't have the documentation in front of me to give you a complete answer, but I believe this is handled by using the SpanIndicator class. Look in the Help file for that and it should have details on how to implement it. Sorry I can't provide more information right now.
Yes Boyd is absolutely correct. You use the SpanIndicator class. We have some implementations of SpanIndicator that draw wave lines. Try using our example SpellingErrorIndicator, which draws blue wave lines.