While traditionally collaborative divorce is thought of applying to the end of marriage, the collaborative process (or something very similar) can be used to help people begin their marriage. Collaborative pre-nuptial agreements are the result of open communication and full disclosure between a future husband and wife.
Both people meet with one attorney, after signing conflict waivers. That attorney ends up officially representing only one of the parties. At the meeting, the attorney explains his/her view of pre-nuptial agreements and works with the parties to come up with an agreement that they want to have drafted. Since it is a requirement of the statutory laws regarding pre-nuptial agreements that the parties fully disclose everything to each other, meeting together with the attorney should not be a problem. After the document is drafted, the parties bring it to another lawyer, who officially represents the other spouse. That lawyer reviews the document with them. If any issues come up, the parties and lawyers meet together to resolve the dispute.
Rather than having the pre-nuptial process cause a rift between the parties, this process allows the parties to work together on the roadmap of their financial future.
I find your concept appealing, but I would be a bit concerned the engaged couple might not truly get that you only represent one of them. Why not bring the other attorney in from the beginning? It seems you get through the agreement after a handful of collaborative meetings.
I like the thought of implementing collaborative prenups.