How to recreate a low shutter speed effect on 1/10000 footage?
Even if the camera has no (suitable?) filter thread, you should be able to fix some Cokin filter holder to a flash bracket.  While I cannot vouch for ready made solutions here, I should be surprised if you cannot combine a few stock components.  The main problem of course when using such a contraption on an ND filter is to prevent side glare.  You might need to work with some light-proof drapings or stuff.  It may be feasible with a flash bracket or similar (macro bracket?) to move the filter right up to the camera, greatly reducing the problem.