I figured it out! unique_names will pass another name param with a new name but S3 and Google Storage ignore that - I give an overview of that finding here: http://www.plupload.com/punbb/viewtopic.php?pid=4306
The solution is to use the key param to set the filename manually for each file. Do this in the UploadFile event where you can change the params for each file that's uploaded on the fly. It would look something like this:
$(function() {
$("#uploader").plupload({
// PreInit events, bound before any internal events
preinit : {
UploadFile: function(up, file) {
up.settings.multipart_params.key = 'plupload/blah'+randomString()+'.jpg';
// You can override settings before the file is uploaded
// up.settings.url = 'upload.php?id=' + file.id;
// up.settings.multipart_params = {param1 : 'value1', param2 : 'value2'};
}
},
......
Hope that helps people!