Azure ACS - Relaying Party Application - ReturnURL with parameters?

We're building an application which uses ACS. Our usage scenario looks like this:

1. The user gets a URL like this one https://our.application.com/?requestId=123456 via email and clicks on it
2. The user gets redirected to the LiveID login screen
3. After logging in, ACS forwards the user to us, but to https://our.application.com/

Unfortunately, it seems that the "Return URL" setting in the "Relaying Party" on the "Access Control Service Portal" is just a fixed string. Is there a way to propagate the original request to it? If not, what would you suggest as a workaround?