Something doesn't sound right as the Magic Pie's rim should not be anywhere near half an inch off centre. Apart from
the original version of the Magic Pie, all other spoked versions
(MPII-MP5) should be properly centred.
I would first check that the forks are not the cause of the problem by fitting the old front wheel and making sure it is centred, and then refit it facing the opposite direction to ensure it is still centred.
If the fork legs themselves are evenly offset, the rim should be properly centred no matter which way around it is fitted.
If it is only properly centred one way around and off centre when fitted the opposite way, I would say that the forks may have been subjected to a side impact and the front wheel has subsequently been adjusted to compensate for it. If this is the case, the forks would need to be either realigned correctly
(apply a little bit of "gentle persuasion" using a long tube) or replaced
(if they cannot be satisfactorily realigned).
If the original wheel rim is properly centred when fitted either way around, the offset problem is probably the result of an assembly error with the Magic Pie.
Make sure that the Magic Pie's axle is located fully into the dropouts on both sides of the forks. If one side is a lot tighter than the other, it might need a little bit of filing on the dropout to allow the axle to fit correctly.
However, if the axle is properly located on both sides, then the rim will need to be re-centred correctly, which you should be able to accomplish by loosening the spokes on the side which is rubbing against the brake pad and tightening the spokes on the other side
(assuming the offset of the flanges in relation to the hub has not been accidentally reversed because the hub has somehow been assembled incorrectly). If the offset on the spoke flanges on the hub looks wrong, please post some pictures and we will hopefully be able to determine the cause of the problem.
If everything seems OK on the hub, I would suggest that you start at the valve and slacken each spoke nipple on the relevant side of the rim one complete turn until you reach the valve again, then tighten each nipple on the opposite side one complete turn until you reach the valve for the second time.
You may have to repeat this process several times
(using smaller or larger adjustments as necessary) until the rim is properly centred within the forks.
Alan 
