I just discovered this. Blogger doesn't have this kind of option, and it annoys me. I found this tutorial that helped me figure out how to do this. I will warn you, you have to scroll about 3/4 of the way down on your Edit Html page to find the code you need to insert your NEW code after.
AND you have to make sure under your settings that you have embedded your comments at the end of your posts instead of on a separate page.
Here's the LINK. Now you can reply to comments!!! Isn't that great?