Hi Lyn,
According to the app's description on iTunes, you can "Import a route or virtual competitor by simply tapping on a GPX, TCX, FIT or KML link or file in Mail or Safari". So, you should be able to simply download the route from plotaroute.com in one of these formats (I would recommend TCX) and then open it in your Cyclemeter app, or alternatively you could download it on your desktop computer and email to your iPhone.
John
Is it possible to download my Plotaroutes into Cyclemeter on my iphone? If so, how!