I'm with englishal on this one - the less playing with altimeter settings the better - I'm sure that there are more important things to do and sooner or later you will just confuse yourself.
The more flying I do in the US the less I am convinced that QFE is necessary. Just lookup the airfield elevation and use QNH.
Below transition altitude it's QNH/QNH for me. Above it's 1013/1013. No room for confusion and it makes the cross check very easy.