How Exclude Users Currently Active in Canvas

Hi there, I'm trying to figure out how to exclude users from getting a Memorial Day Promotion who are currently active in our Welcome Series Canvas (that lasts ~30 days). 

What's the best way to do this? Feels like I can't use last received canvas step messages less than 31 days ago, because the user might not be in the Welcome Canvas that long if they convert. Also can't use User Update custom attributes, because if they convert from the canvas, I can't update their profile on conversion in the same canvas right?

Please help - this feels like a simple request, yet it's proving to be quite complex.