There's no such thing as a dual seat for a SL/FE.
There are supports underneath the rider's seat and at the back near the lights. The front supports are designed to take the weight of the rider but the back ones probably won't take the weight of a pillion.
See here for some piccies.
http://www.ducatisportingclub.com/at...8&d=1158775514 If you want to carry a pillion on an SL, the entire rear section swaps over from a standard SS. These parts should be available fairly easily and cheap (eg from DD racers) and can be changed over in about half an hour and a cup of tea.
If you want to keep the high level cans then those are the right footpegs to use - but don't expect your pillions to thank you!
hope this helps.
Chi