I want to provide users with the ability to cancel an existing file upload, is there any workaround to allow this?
Starting with version 0.6.1 there is...
If you upload your file like this:
var uploader = new Slingshot.Upload("myFileUploads");
uploader.send(document.getElementById('input').files[0]);
Then you can abort it with:
uploader.xhr.abort();