It should be possible on a non-redemption booking as long as it one where the two legs are independently priced. I think this is now the case for short-haul flights. This is because, whilst you think you are booking a return, you are actually booking two singles and not flying one has no impact on the other, even if on the same PNR.

(Ryanair 100% works like this and flying or not flying one leg makes no difference to the others.)

It won't work if you book a flight where the price of the second leg is dependant on the first - ie if there is a Saturday night stay rule. This is usually the case for long-hauls, except for fully flexible tickets - although even then, on a long haul, I'm not sure if they keep the return open.

What this means for Air Miles tickets I have no idea ....