If I understand your question, There are several custom smart apps that can have one smart dimmer device follow another. I think trendsetter is the most popular right now, but there are couple of others as well. You will find them in the community – created wiki in the quick browse lists on the Lighting list.
If you haven’t used custom code before, it’s pretty straightforward – – you’re basically going to copy the author’s code and paste it into your own account. Here’s the FAQ on that process:
The other alternative is to use webcore. This is a very powerful community – created rules engine and can definitely let you do this. I just think it might be overkill for this particular use case.