How do I "print" from PhP in a cross-domain sort of way?

Question

I'm developing a mobile application and am having trouble debugging my server-side code. I make cross-domain AJAX requests from the app. Normally, I would use var_dump() to display the contents of variables to the browser, but with these cross-domain requests, I can't figure out how to do something similar. What are some common methods that one might use to visualize what happens within the server-side script from a cross-domain perspective?

Here is the bulk of what my AJAX requests look like:

$.ajax({
        async: false,
        url: 'http://mysecretsite.com/page.php',
        data: mySecretData,
        dataType: 'jsonp',
        jsonp: 'callback',
        jsonpCallback: 'mySecretCallback',
        success: function(){
            alert("success");
        },
        error: function(xhr, status, errorThrown){
            alert("Oops: " + status);
        },
        complete: function(){
            alert("complete");
        }
});