Well, I can't do anything about it, it's Opencaching which is open and shares all the data with everybody

I'm not asking anyone their OC password to identify them. It might be possible to devise some way to do it (not easily for me), but that wouldn't change the fact that all this data is for anyone to grab. Just entering somebody's OC profile you can see where and when he was in the past just by listing caches found. It even offers the possibility to export this data in easily parsable form, like gpx or kml. Simply dropping it into Google Maps would yield similar result.
Bottom line - it is something which could be resolved in a meaningful way only on OC end