I just re-read the question. If the sliders really have different sysex ranges, you cannot do this in MD currently. You could make, say, the X parameter control something different depending on the state of a button (by altering its channel) but you cannot have it control something different within MD. For now, this may be a suggestion rather than a question, I think. How different are the sysex sliders that you want to control?
This would be an awesome suggestion, however.
Thanks for the dialogue.