Jim, since your flooring is already installed your best bet is to make a simple guide strip for the router to ride on. I suggest using 1/4" tempered hardboard for this and following the edge with a guide bushing. Fasten it down with double sided carpet tape, the cheapest you can find since it only needs to hold for a few minutes. This assures you will have a clean finished edge.
"Living in the D" (this means Detroit!)
"It's fine to disagree with other members as long as you respect their opinions"