Then you still would have the bunch of actual challenges that do not have the word "Challenge" in the title. If you want to have a correct map, then you have to get those caches in the map, too.
Maybe you, toonburner, can spent your spare time to make, edit and take care of a list of all those caches.
Then the Project-GC Team would love to add this time-killing feature to their site, i am sure.
Seriously: i don't think, that anyone would have the time or the possibility to check every single cache whether it is a challenge, or not.
So, the only reasonable way to get a glimpse of correct data is to go by cache title. Maybe you could ask the cache-owner to remove the word challenge from their cache titles, toonburner.
(i just want to point out, what an impossible task your question would be)