Focus magnify on OMD with legacy lenses or "ordinary" extension tubes?

Can anyone tell me if it's possible, and if so how, to use the focus magnify on an OMD with a legacy lens which has no electrical connections in the lens?

I've got several situations where I would like to be able to do this -- some legacy leica glass and MFT lenses used with simple extension tubes which don't have the electrical connections.

I've got MF mapped to Fn2 and Focus Enhance turned on, but since the camera doesn't detect any focus ring movement it doesn't do anything.