It is not exactly the solution you are seeking. I haven’t found a way yet to do exactly what you are describing in your original statement, but I think that would be a very useful feature. I am also struggling with fairly long comments in my documents.
What I did to kind of circumvent this problem is to lower the User Interface Scaling in Tool>Options>LibreOffice>View>Interface Scaling>Scaling. This has made the display of long notes better in my environment. I’m running LibreOffice 4.2 in Ubuntu 13.10.
Could be a good idea to post your question as a wished feature somewhere on LibreOffice forums I think.