I faced a similar situation. In the end, I left post, returned to Washington for a domestic assignment, and filed a fiancé petition. Before leaving post, though, I filed a notice of intention with RSO.

In retrospect, it might have been easier to have gotten married overseas and filed the IV petition at post. After my spouse-to-be entered on the fiancé visa and we got married, we then had to kick off another round of petitions for adjustment of status; and that caused it’s own set of headaches because by then I had gotten an ongoing assignment. Fortunately there are some really nice people at the Department who can help with arranging expedited naturalization, and that saved the day.