Like many poster's have said, it isn't a perfect world, and there may not be a perfect solution that suits everyone.
One thing to consider with installing longer replacement valve stems on the inside rear duals is that those wheels can no longer be used on the front, because the new longer rigid valve stem well stick out too far. Nor can they be used on the outside rear, because the valve stem will protrude back too far. The rims with the longer valve stems would be relegated to inside dual duty only.
I recently experienced a situation while towing on the highway where this would have been a problem. After a blowout where the spare tire was not available, I needed to use one of the rear tires on the front to get back to home base. So in addition to one of the rear duals having to go up front... the remaining rear dual needed to be in the outside position, as recommended whenever temporarily singling out a rear dually pair.
In both cases, I was thankful that all of my valve stems were the same, as it made all the wheels interchangeable in all positions.
This type of flexibility is likely not needed by everyone, but it is something to consider if you think you it might apply to you.