You don't need SLI for multiple screens, In fact, until a little while ago, you couldn't have more than two (or in some cases 1) screen while using SLI, you just needed multiple video cards.
If your motherboard can accomodate more than one video card, then it might be able to use them both.


I wouldn't take my word for it as all motherboards are different, as are video cards, but it has worked for me in the past.
I would recommend (if possible) testing it with a friends video card and see if it works