Comment by cmatteri

Shouldn't the mill be able to precisely drill very small holes for you? Perhaps you could you use the pick and place machine to put small pins in the holes which would be soldered in place on both sides. You could conceivably use one 2-layer board and two 1-layer boards, each with alignment holes drilled in them, pins inserted and solder paste applied to make a 4-layer board. There would be a thin gap between the boards, but since everything is soldered together, would it matter?