Nope. Railgun needs both endpoints functioning to make that speeded up connection. From the support document: "Unlike other Cloudflare features, it does require a program to be installed on or near the origin web server. "
I don’t believe you can even activate Railgun if a server hasn’t been set up.
Also, nothing can directly increase the speed of third-party scripts like adsense, as the browser itself makes a request to Google’s servers. Ad load times are entirely dependent on how fast Google can bid and serve an ad to the browser, and how fast the browser can render your webpage.