As you noted, the models with two chains all have freewheels. Further, the mid drives are nearly all made with geared motors; they will also freewheel.
I am left wondering, what model of mid-drive do you have that doesn't freewheel?
The only one I can think of is the old "stroke-monkey" design. I would never recommend one, like that, that has a non-geared motor directly coupled to the bottom bracket. It has been off the market for some time, I saw it as being unsafe.
Now, if you mean an honest "zero" drag; it cant't exist. Even magnetic bearings, that cannot function anywhere but the most controlled environments, have some drag.