At this point in the building process, the idea of having to rout a perfect circle of a perfect width out of my soundboard was a little intimidating--there's really no room for error here. The book talks about dry fitting the purflings and inlays and then pulling it all out and glueing it all in again with wood glue in one swift step. Instead, it was recommended to me to take my time fitting all the strips, and then covering the top with a watery super glue, allowing the glue to "wick" down among the strips. That way I would be sure the purflings aligned properly. This actually worked brilliantly, and I can't imagine the hassle of using wood glue for this step (it took me hours to fit all the strips in properly).
Lastly I spent a little while planing down the rough rosewood to approximately the soundboard level, and then finished it off with a scraper (leaving just a microscopic amount for "final sanding").