As far as I know this is not possible.
My suggested workaround would be to use the mentioned module called "Solved Mysteries" and combine it with the Virtual GPS and/or bookmark-lists depending on what you want to do.
So, create a virtual GPS, use Solved Mysteries to add all your solved mysteries to the Virtual GPS. Create a bookmark list, export the virtual GPS to the bookmark list.
If you want to show all unsolved mysteries in your region, use MapCompare, select the cache type filter to show only mysteries, use the filter "ignore bookmark list" to ignore the bookmark list filled with your solved mysteries and select "none found" and "owned as found" and the region you want. This should give you a map of only unsolved mysteries in the area.
If you want to be able to plan a route but don't get distracted by all the unsolved mysteries I usually make a new Virtual GPS, start by importing the solved mysteries and then do the MapCompare with all cache types except mysteries so I don't have to see all the unsolved ones.
Both Virtual GPS and Bookmark lists can be used as filters in for example MapCompare.