You probably don't need to move your ordering values out to a different table, unless they will be used in multiple places and have a different position depending on which list they're in.
Usually, I find, the easiest solution to this is to use a signed integer, call it 'weight' and default weight values to 0. Then as things are reordered lower values float to the top, and higher values sink to the bottom.
In that way you can simply order by weight ASC and have the explicitly defined order, with non-explicitly set items falling where they may in the list. Or you could order by weight then by post date, or title, or some other secondary sort.
Anyway, no.. I don't think a pivot table is necessary here at all.