@Chewing
Keep in mind that you can automate the send to a bus as well as the volume fader on the bus itself.
So, one easy way to manually do this is to select the bus with the delay on it and swipe in the lower half of the track during verses and reduce the volume of the delay to where you want it. Then bring it up between with a nice slide. If you hover your mouse pointer at the top of the track over a selected region you can click and drag and envelope nodes will be added at either end of the selection making this easy.
A side-effect of this method is that you will get whatever words in your delay that were sung.
If you do this instead with the send level, you have strict control over the volumes of certain words, regardless of where they might fall in the delay. So a low priority word can be ping ponging left and right at a low volume and a high priority word can ping pong more strongly without raising the lingering volume of the low priority word.