I know this might be abit too late but there is a better more flexible way to do this, although it's not actually combining the two entities but rather more of a visual effect.
It's called using Overrules. Basically you change the way the entity is displayed. So instead of displaying a line, you can display a circle, or in your case display a text and a line.
Overruling is a very powerful tool, you can not only change how the entity looks but also add grips, remove grips, change how entity is highlighted or highlight other entities when your entity is highlighted, override some of the entity methods like erase and much more.
Best place to start from is Kean Walmsley's "Through the Interface" blog.
And here is a link to this blog related to what you want to achieve
http://through-the-interface.typepad.com/through_the_interface/2009/08/a-simple-overrule-to-change-the-way-autocad-lines-are-displayed-using-net.html