To be honest if your going to go to the trouble of having a vow and dance and party celebration and you want to be called husband and wife then just hire a celebrant and be official. Kinda pointless for all the other stuff then IMO
I don't really see it as pointless because the symbolic gesture of promising myself to somebody for life is what means something to me and doesnt need a government stamp nor fit in with their definitions so would just feel odd to include that part. It would be like a nonreligious person using vows that included God, I don't really believe in the government defined marriage but I believe in my lifetime with DP.