Perhaps Stephan and I do not understand your problem. Left and right side is problematic terminology. Try long side and short side and then left, right, top and bottom to further describe what you are trying to do.

With all pages landscape, Word has no problems reserving a binding area on the short side of the page. It is unusual, although not unheard of, to bind landscape documents this way. That is, the left (short) edge of the odd-numbered pages has extra room; the right (short) edge of even-numbered pages likewise. I expect that this is what Stefan meant when he said you should have no problem. (This is the same kind of mirrored margins used in portrait-orientation.) The standard mirrored margins command fails with documents containing mixed orientations.

Anything different from this, or in documents with mixed-orientation pages requires use of different even and odd headers/footers with spacing reserved in those. See Mirrored Margins with Landscape for a discussion of what is involved.