Well, "relatively easy" is a relative judgement, and all I can say is, "It depends on what you define as 'easy'".
4' is a long way to keep the bit straight. I would personally try using an aggressive spade bit on a 24" extender, and run through from each end towards the middle. I would do this by rigging up a jig to hold the 4x4 vertically stable on a drill press frame, and again, only do half the depth before flipping it over to drill from the other end.
4' is a long way to keep the bit straight. I would personally try using an aggressive spade bit on a 24" extender, and run through from each end towards the middle. I would do this by rigging up a jig to hold the 4x4 vertically stable on a drill press frame, and again, only do half the depth before flipping it over to drill from the other end.