I figured out a way to do this. onclick event for the Next/Previous buttons does a document.getElementById("spaLoading").style.display="inline";
Then for the AfterRenderJavascript, have it call a function that sets the above span's display to "none". This enables a "Loading..Please wait" message to appear while the calendar renders the new data and then it goes away once it is complete. This should help prevent the users from pressing the next/prev buttons multiple times.