FSnav may have an export module However I use http://rfinder.asalink.net/ As a subscribing member I can make a route, save it to the PMDG format, and load the plan with the PMDG FMC.
Well the route generated by routefinder (link above) did have a flaw: Arrival airport didn't have elevation data so it was a hazzle to get VNAV to work :)