Making the Grigri's cam absorb most of the friction by finding the sweet spot of its lever, if this device is employed.
Strictly speaking of what I do when lowering a climber on belay, I agree with the first one - let grigri absorb all the friction.
I prefer placing the guide hand under the brake hand, that allows me to maintain a slow and steady feed of rope. With a steady feed the likelihood of sustaining major skin-burns due to friction is less. With an inconsistent/jerky feed, you may burn your hand badly.
Secondly, I prefer keeping the thumb of the brake hand upwards, as in towards the device, that allows better control.
Just a note, irrespective of lowering a climber or belaying him/her during a tope rope ascent, keep the brake hand a safe distance away from the belay device so that in case of an unforeseen fall your hands wouldn't lead to getting pinched in the device.
Making your leg/clothes absorb part of the friction
I don't see how effective it is going to be. I'd rather focus on the point above. IMO, the legs would come in play for absorbing the dynamic falls over a climber during an ascent. Your body should/will act as a counterweight, using your legs to push against the wall will prevent any injuries and catches a heavy fall better.
Using a kind of Prusik knot under your braking hand so it absorbs friction.
I haven't seen such a setup, but if I interpret your arrangement here - you'd attach the prussik to rope where you want to your brake hand and the other end is attached to your harness? If yes, I don't see why that would help. Because, if the hand of prussik goes off the rope for whatever reason, if the length is not managed carefully, the prussik will lock but lead towards the device, making things worst.
I have seen using prussik on the guide hand (loaded end of the rope) for better control, but I have never used it. It is something that I'll try tomorrow and see how it works! :-)
Hope this helps.