Crazy need to ENABLE cross site scripting

What are asking for isn't cross-site scripting (which is a type of security vulnerability in which user input (e.g. from the URL) is injected into the page in such a way that third party scripts could be added via a link).

If you just want to run a script on a different server, then just use an absolute URI.

<script src="http://example.com/foo.js"></script>

If you need to perform Ajax requests to a remote server, use CORS or run a proxy on the current origin.

Again, this is for testing only

Just for testing, look at Charles Proxy. It's Map Remote feature allows you to (transparently) forward some requests to a remote server (based on wild card URL matching).

What you need is just a little passthrough service running on the first server that passes requests over to the second server, and returns the results it gets back from the second server.

You don't say what language the server side of your application is written in or what kind of data is passed to or returned from your service, so I can't be more specific than that, but it really should be about 15 lines of code to write the passthrough service.