Can I enter into a contract to get married to a specific person by a specific date?

I am an American looking to get married to someone on an H1B Visa. We cannot get married until after a certain date to avoid interfering with her visa extension process. However, her parents want us to get married much sooner and will not accept going through a marriage ceremony without becoming legally married as they don't trust Americans. In order to satisfy everyone involved, we thought we could sign a contract that says we will get married by a specific date in the future (where it would not interfere with the extension process) as proof of our intention to marry. If this is a possibility, what process should we use to do this? Should we write the contract or hire a lawyer to do so? What else should we consider in doing this? I understand the somewhat ridiculous nature of the situation, but I hope someone can help us navigate it. If this is something we can do, it would make our lives much easier.