I'm not sure if i understand exactly what you mean...a drawing might help.
Regarding collision detection: Sorry, but i'm not going to add any other means of collision detection and i'm not sure what the problem with ellipsoid collision detection should be!? It's the only approach that lets you climb stairs or obstacles reliable. It might be needed to tweak the parameters to match your scene though. It might also be unwanted that it collides with the actual geometry of the collision target but in that case, you can use collision meshes instead (there's no build-in support for this, you have to code it yourself), i.e. a simplified mesh that is used for collision detection only. In my RPG thing, i'm using this for fences and NPCs to prevent the player from climbing up on NPCs...
I simply have an option in my views to enable collision meshs. In that case, i calculate a bounding box of the mesh and add it as a child. Before a collision detection, i set the object to invisible and the collision mesh to visible, do the collision detection and reverse the setting.