It seems to me that it would be ideal of manpower and equipment both flowed along supply lines (for simplicity, using the same network) to their units. Then, as Joppos said, a player could create "paper" units anywhere with zero men and zero equipment, which would be resupplied as normal. This allows a player to decide whether they want to place new units at the front, creating a steady influx of reinforcement there, or to place them at home and then move the units en masse when they are at full strength. Such a system would also allow the splitting of various kinds of manpower, if that is desirable (which I think is an entirely different argument).
One issue with this is that supplies cannot, at least on the Hearts of Iron 3 model, flow "in reverse." So if partial division A is at the front and then you place zero-manpower, zero-equipment division B behind it, you cannot disband division A to fill division B; the manpower and equipment will teleport to the capital and then flow across the supply lines back to the front. I think this is an acceptable abstraction, though, especially if we can merge divisions.