Best way to dynamically exclude survey respondents from a Journey Orchestrator reminder send?

New to gainsight here so still learning some of the ropes but wanted to ask for some help on automation.

We're running a reminder email program in Journey Orchestrator for a survey campaign. Each recipient gets a Typeform link with a unique trackid embedded as a tokenized field, so we can tie a submission back to the original recipient.

The problem: people who've already completed the survey are still getting the reminder, because there's currently no automated way to pull them out of the next send before it goes.

What I'd like to build: when someone submits the Typeform, that updates a field in Gainsight against that trackid/identifier that then says they did the survey. I’d use that field in an evaluation step to then exclude those from the send of the reminder email a week later. 

I know the Program-level Exclusion List is CSV-upload only, so that's not a fit for something that needs to update continuously. Would love to hear if anyone's done a Typeform (or similar external form) → Gainsight integration like this and has lessons learned.