Yes, you can that with RAW video:
-Load mlv_rec, restart camera
-Get into x5 mode
-Enable "RAW video (MLV)"
-Highlight "RAW video (MLV)", then press Q button, select 960x540 resolution (16:9 AR)
That resolution would ~match x5 mode preview.
You can reduce FPS to 23.976 using FPS override if you want continuous recording (required write speed would be 20.7 MB/s). Also you can lower aspect ratio or resolution more.