Hey mangoman!
If you email support@Beeminder.com, we can set that up for you. Custom aggregation methods are officially part of the Bee Plus subscription perqs.
But I think yours is a fine example of a special case. Those location-based triggers sometimes go mental and trigger far more than a human might expect. (And occasionally, less often, i.e. zero.)
Update: I’ve gone ahead and changed the aggregation method to ‘max’, so although the extra datapoints will still arrive, all of those 1’s will only count as one visit to the gym that day.