You will need papers from home. The Etat Civil (civil registry) can't stop them from issuing your D visa. Anyway, a D visa is only an entry visa which you won't get until your work permission gets approved.
Are you within your allotted time to be in the country? I assume you are on a tourist visa right now. Have you over run your 90 days?
You should tell them up from. "Hi, I'm in the process of getting my D visa because I am moving here for a job. When this is finished and once I move here, me and my fiance(e) want to get married. What do we need to do? What papers do we need to provide you?".
You are making it more difficult than it needs to be.
In the meantime, you may want to read this to see if it helps.
http://www.bj.admin.ch/content/bj/fr...d/faq/ehe.html