Our only tool for converting generic objects to Land F/X objects is the Mimic (Match Properties) function.
As of now, we have not added the ability to convert a generic line/polyline to pipe. It would require scanning the area near each end-point, and connecting the pipe to each object. Certainly possible, it would just take some time to develop. In simple, perfect scenarios, it should have no problem correctly connecting to two recently converted emitters. But intersections, pipe hops, and other nearby objects would all present problems. So should it then highlight the areas it was unable to determine how to connect a segment of pipe? Now that's even more development.
We've only been asked about this a couple of times, and each time those users ended up just re-piping the system quickly enough -- and certainly quicker than the development time necessary to create such a tool.
This is something we can certainly consider for development next year. If you could send in the plan in question, we can investigate it to see if there is a possibility to do anything sooner.