There is actually a setting in Donor Central that controls this behavior. To update:
  1. Go to Site Configuration > Admin Portal
  2. Click on the Fund Summary Settings Link.
  3. Set ‘Keep Pending Suggestions Until Paid’ to Yes.
  4. Enter a date for ‘Pending Suggestion Date’ that is a few months in the past.
  5. Click 'Submit Setup Changes' and wait for a confirmation.
Now the Grant Suggestion will stay in Pending Suggestions until you approve and post it in FIMS.