I think what you are proposing will theoretically work....a "c" shaped date wheel that wraps around any overlapping gears and has an overall height that reaches the backside of the dial. Like this....
However I think the manufacture and modifications to the required parts will be so difficult that it probably isn't worth doing. Firstly the upper date wheel will have to be slightly thinner then the first plate to be able to clear the second plate gear train and also stay below the backside of the dial (not sure if they are normally that thin so you may have to make one). The first plate will have to be cut back far enough to accomidate the width of the date wheel since it will reside at the same level. Then the real trick.... in order to assemble/disassemble the movement the attachment of the two date wheels would need to be done so that you can actually get them appart. I suppose you could glue them as you built up the movement but you will never get it apart again....at least not without breaking it.
It would be fun to mess around with for sure. Let us know if you give it a shot.