There as bunch of ways to show super strenght, depending on what suits you. Using keying (similar to posted tutorial) seems easiest: you can have person pick another up with one hand, or even do one-hand inverted push-ups
Without compositing (no green screen/garbage mate) I would recommend you see this: http://www.theforce.net/fanfilms/nonsw/grayson/
Watch the trailer and see how Superman picks up a vehicle. Then watch the BTS and see how it was done. No digital tampering.
BTW, his BTS is great really