There are 4 exceptions to the joint filing requirements of the Form I-751.
- Death of the US citizen spouse
- Battery or Extreme Cruelty
- Evidence that removal would result in extreme hardship
There is no separate form for this waiver. The petitioner needs to just show the evidence and request the waiver. The forms have been updated recently and the relevant sections can be checked off. Checking off more than one is possible, but it might be advantageous to check one or the other rather than both depending on the circumstances.
It is still required, however, that the petitioner show that they were in a bona fide marriage. This is crucial to any waiver case.