sure, possible. I just two days ago created new part of code called "TrackNavigationGenerator". It should have simple purpose. I take track from GPX and put it inside. Result should be same track, together with many waypoints that will have attached these parameters, like rtePointAction etc. So exactly same parameters I generate from track you compute over mapQuest etc. So probably similar to what you do.
I have this already in mind and it should be quite simple. Every track in locus will have button "navigate". If this will be pre-computed (mapQuest, cloudmade, ...) it will work as normal navigation. If not, it will in first step go through "TrackNavigationGenerator" and then .. voala, normal navigation
I was just stuck on start, so not much work is done yet