custom left-right, right-left content animation treatment across multiple layers

Hi Heroes. I have a thorny  SL problem (for me at least, somebody probably has this down cold). I'm not a heavy user, and this community provides such great support; I'm hoping someone can help. I have a 5-panel click-through interaction on a slide using layers for each panel, and am trying to achieve the effect where, no matter which layer you access a layer from (e.g., from 2 to 3 or from 4 to 3), the existing panel's/layer's content will slide out (to the left or right, depending on whether the user is ascending or descending in the layer sequence) and new panel's/layer's content will slide in (from the left or right, depending). 'Got myself all tied up in a logic pretzel trying to work this one out... If this isn't making sense, please see the illustration/diagram. My sense is this is a fairly standard treatment but I haven't been able to create it based on my SL knowledge, which is OK I think but not awesome.