Calculate Average CSAT for Scorecard Metric

I'd like to calculate an average CSAT score for surveys submitted in the last 180 days for a scorecard metric. We have this set up for NPS but obviously without a standard CSAT question (I know that is under consideration) I'm not sure how to go about setting a similar metric. Is there a way I could assign each of our 5 CSAT responses a 'score' and then average them for the account? I don't want to just use the most recent response since that wouldn't give us the full picture if multiple users complete the survey in a short time frame.