I think I would be tempted to construct it from large triangles of a single colour so the seams form a zigzag across the width of the runner and become something of a feature, especially if you top stitch either side of the seams using a contrasting colour (a metallic thread perhaps?).
Or perhaps you could suggest shorter table runners that go across the width of the table rather than along the length (one for each pair of facing place settings)?
Yes, two or three stripes of ribbon at either end then one in the middle to cover the join. You could do one two inches from the end, the next one three inches above that then the next one four inches above that one or place them all at equal distances.
Lay the cut runner pieces down, pin the middle ribbon in place then experiment with placing the other pieces.
I've been asked to make a plain 6 foot table runner for a friend who has a red and cream room so she wants it to coordinate. She had asked for it to be one colour, but I don't think I'll be able to find a width of fabric long enough (and she doesn't really want to spend the money for me to buy the length of fabric) to do it in one go. Are there any clever ideas to 'hide' the seam? I wondered about either doing it in two lengths of red sewn together, and then something appliquéd into the middle in cream, or will that look odd? Or triangles of each colour the whole way? She's keen on something plain...