Lend me your brains

With a freewheel the tensioner only prevents the chain from jumping off, doesn't actually take the strain of the drivetrain (which is on the 'top' of a conventional chainline).
So a single tensioner on the right hand side, used with the leftie drivetrain set at correct tension would be okay.. right?

Yeah I reckon so, although it would look gash and (in theory) it would be possible to figure out the magic gears anyway...

I'm thinking that the real issue will be in the time it takes for the freewheels to engage, making the braking side feel like mush, and possibly something odd going on with inertia as Brucy said.