Here is what I did. I added these types of calls throughout the different macros that run during the "activation" flow of a source.
Code:
SetVariable|{{activeroom_{{clientname}}}}_poweron_progress~5!
.
.
.
SetVariable|{{activeroom_{{clientname}}}}_poweron_progress~25!
The value is the percentage complete and I just made up the percentage complete numbers. I just wanted to show that things were moving forward so it didn't need to be super accurate. Then I added the progress bar component to the overlay and set the variable field to, {{{{activeroom_{{clientname}}}}_poweron_progress}}. But as I mentioned I did have some trouble with that so in the end I just did the substitution manually because I only have one room that I'm using this remote for. So it ended up being {{theater_poweron_progress}}.
You can see what it looks like in the video below: