No, multiple super controls, each controlling their own single variable within a SysEx message -- that would be the ideal.
If this were the case, you could have a single fader that sends a SysEx message when pressed. But the exact message it sends would be modifiable by a group of other super controls.
The generic SyseEx message sent by the fader could be, for example:
Company ID, Product ID, Individual ID, Parameter Group, Parameter Number, Parameter Value.
The Company ID and Product ID wouldn't change, and so would be entered into the fader's MIDI as static hex bytes. The Parameter Value would be the V variable, as now. But the Individual ID, Parameter Group, and Parameter Number would be the variables L, M, and N, and these would be obtained from the settings of three Super Controls A, B, and C, respectively. So you would "steer" the message to a specific parameter target using Super Controls A, B, and C, and then use the fader to send the value to the targeted parameter.
In this example there are two additional variables M and N beyond the currently available V and L. But really, even just one additional variable M would help a great deal. Any additional variables beyond that would very nice, but I don't mean to suggest I would be asking for the most general case where you could have any number of additional variables. Just one or perhaps two more would be extremely flexible.
Sounds like you've already got this on the Features To Add Someday list, so I'll look forward to that!
Thanks