greenimi,
This solution would be the last I would use and recommend in this case, unless there is really a functional need to define something working along dynamic-profile-tolerance-zone lines. The reason I came up with this method was that in the 2009 version of the standard there is no tool that would work similarly to "dynamic tolerance zone" modifier (as proposed in the new draft of Y14.5). The tricky part of it is that hex contour is not fully defined with basic dimensions, and so many people may see this as a violation of the profile tolerance application rules. I personally think it is more like extension of principles (supported by the infamous figures from the standard where cones are controlled by combination of directly toleranced +/- diameter and profile tolerance).
With that said there are at least couple other ways to control hex features, and most likely at least one of them will grasp the design intent (some of them have been already mentioned):
1.Three position feature control frames applied to each pair of parallel faces and referencing to A. Tricky part of it: inspection will have to know that these position callouts apply simultaneously, so in fact the angles between center planes of pairs of faces are also indirectly controlled.
2. Simple all-around profile callout wrt A.
3. Composite all-around profile callout with upper segment referencing A (location control) and lower segment with or without A (size/form, or size/form/orientation control).
4. Combination of datumless all-around profile tolerance and position at MMC.
5. Combination of datumless all-around profile tolerance applied directly to hex contour and position at MMC wrt A applied to a phantom maximum inscribed circle.
6. A little bit more tricky application of combination of datumless all-around profile tolerance applied directly to hex contour and position at RFS wrt A applied to a phantom maximum inscribed circle.