You...really don't like the evasion clause, do you?
But that's not important. I'll try to help you with your Zen Mode Darmanitan. If I was gonna EV train one, I'd think training it in Defense and Sp.Defense would be best, to maximize its defensive capabilities. Or you pick which side you wanna tank, physical or special, then put the EVs into HP and the defensive stat you picked. One of those should hopefully get it down to Zen Mode HP range without endangering it too much. It might be able to make use of Roar and Toxic.
The hard part about using it is that it'll revert to regular mode if its HP goes over 50%, but Leftovers still might be useful since it'll be taking hits anyway.
You're probably gonna just have to test it out on Showdown or something a lot, learn by trial and error.