I... think you can, yeah.
good god this game just goes on forever... I think I messed something up, is it still possible to shag Leliana if you haven't done her personal quest after the landsmeet has started?
Leliana's a little buggy, anyway. I think if you get her approval too high, a certain dialogue option disappears, and you need to lower it again in order to get it back.
Just... don't finish the landsmeet until you've made sure. And if you've already finished the landsmeet, don't go back to Redcliffe.
EDIT: Dammit, Ryuu.