There are several threads talking about this. Use the search.
The short version: if you want tracking of all 7 strings at the same time (as in not having 2 strings share 1 output, like Conklin does), you're screwed. Unless you're brave and rich enough to put TWO Roland systems into that guitar, TWO cables and TWO sets of controllers. IIRC, all the Roland-ready gear only works with 6 signals.
AFAIK you can use a piezo system to act as midi triggers. Conklin have been using that system for quite some time on variedly stringed instruments ( 9 strings and over). Finding piezo saddles should be easy, maybe you can contact Conklin and find more about their circuits or ask them if they could just sell you the guts.
The problem still exists, even with piezos. It's a limitation of the Roland system, and there aren't really any alternatives. Last time I checked, Conklin guitars >6 strings share outputs, and the outputs are monophonic.