I don't think anyone is going to specifically advise that you do this. Without doing any research myself, I'll give you a couple things to think about:
First, the only way to change the number of lugs out back is to change the axle shaft to one of the new ones with 6 lugs. This would probably be pretty expensive, if it can even be done (need to make sure the number of splines and shaft diameter and length all match)
Second, if you don't change the back to 6-lug, you'll have different wheels front & back? Not sure what the end game is here.
Third, (assuming you have 2WD) the front brake rotor/hub assembly is all one piece, and you could simply replace it with a 6-lug rotor/hub assembly if the spindle geometry was the same (diameter, taper, length, etc). Only way I know to find out for sure is to install one and check to make sure it spins tight and true.