Can your fiancee fly to you? You can do marriage registration in Thai embassy, get single entry 3 months Non-O visa from the same embassy and get back with her.
I do it like this (I live in Thailand with my Thai wife and have company in my citizenship country). In immigration office they told me that I don't need work permit. I have customers only in my country, so it doesn't affect Thai labour market at all. I extend my stay every year (3 times already), everytime I bring them documents that I have company in my country and they never said a word about work permit.