As Georgy Gobozov stated in the comment: The answer to your question is "No".
If you are using the standard portlet request handling and rely on event handling, you're bound to a full page reload. There's nothing that keeps you from implementing custom event handling (e.g. with JS on the browser, through your business layer etc.) but unfortunately you'll have to do exactly this.
When you start the original request, e.g. through an action handler, the page has already started to reload (from the browser perspective). Any attempt to cancel the processing server side will result in the stream to break and the browser signalling an error on the page (e.g. "can't load": The result must come with an HTTP status - and it will most likely be an error code (e.g. 50x), or it must contain the whole page's HTML.