Solution: Custom game --> Turn bots off --> win
Atleast I guess you can do it this way.
Otherwise:
Custom game --> Do 6v7 with bots, you are the 7th person --> stay in spectator mode (If there is one)
An easy and effective way to do it.
"Going into levels and playing against players who know the map like the back of their hand is a real problem. And so you're really at a disadvantage. So what do we do? We integrate a system where you can, at a glance, look at this objective wheel, see everything that you can possibly do in a given mission, choose one, and then there are systems within the game that will help you find your way there no matter what." - Richard Hamm
It seems like they don't want you knowing the maps. Thats the point of the objective wheel. You shouldn't have to know the maps in order to be good at the game. On the same token, they might be designing levels to the point where it doesn't matter if you know the area because there aren't any "secret" or "hard to reach" areas.
Even then I would go explore the maps, its not like the devs want you to follow preset routes, certain exceptions apply of course.
There are 2 types of those "secret" areas you speak of. The one is intentional. It exists with the devs knowing about it and is deliberately in the game. The scond type is unintentional - leftover or overlooked by devs/testers, and usually exploited by players. These areas, when discovered (and depending how exploitable they are) are usually fixed post-launch.
By definition, secret areas come with an expiration date, since once they are discovered, their whereabouts become known and they are no longer secret. Also, just because an area is "secret" doesn't necessarily mean it is a good spot.
Agreed secret is not always good. That's one of the ways you improve is seeing what spots people use then when they become the norm people find new ones or really old ones.