You know what.. the old guy that showed me this exercise asked me how I would practise without a guitar and I basically told him the same thing, "Air-guitar".
I can't take all the credit for this exercise but it seems that VERY FEW people I ever speak to actually knows how to practise guitar without a guitar. I'm glad my little contribution to the guitar world is a bit helpful.
(We'll call it the "Budd finger exercise" just cause I don't know the name of the old guy I learned this from

)