Nicky you are correct. Only @ 25% of the US States permit same sex marriage or civil unions however I have performed services for couples who desire a spiritual connection. It's not legally binding but similar benefits can be realized through legal channels.
The service I do talks of love, commitment and respect and of the spiritual and humanistic bonds that are above the jurisdiction of any government. I have a long conversation with each participant so I get to know them as much as possible, then base the service on how they perceive their future. I rarely mention god unless specifically asked to include references to the deity which they embrace. I stress that spirituality supersedes laws of the state.