FCPX is not the app to handle something like that.
Motion isn't that helpful here as well.
Additionally the Apple DV Codec is poor (always had been) and makes the fields a bit blurry.
You can do it with AfterEffects - but even there it's a bit tricky.
Import the clip twice (as 30 fps), for one interpret footage as lower field first for the other one upper field first. Set the interpolation to something like "field changes" - I can't remember and don't have access at the moment.
Put them both in a comp and slow down to 50% duplicating the frames.
Switch off the version with upper field (that's the one which contains all even frames in motion)
Render the comp as image sequence to a folder named yourFile-even_frames.
Go back and switch on the upper field version and off the lower field one.
Render the comp again as image sequence to a folder named yourFile-odd_frames.
In the yourFile-even_frames folder remove all images with odd frame numbers - can be done by a simple script.
Copy the left images to the folder yourFile-odd_frames replacing the files with same names.
Now the real tricky part if you want to have nice ghosting (which can be done in Motion as well I think):
Import the image sequence as 60 fps and create a comp for that with 4 times the duration.
Now slow down the image sequence to 25% to match the duration but use optical flow or Twixtor.
Render out again - you can put that comp into another comp as well.
Now speed up the resulting movie 400% to get the original length at 60 fps using motion blur/optical flow.