You'd have to do it manually.

In the fileQueued event you get a file object that has the file size. You'd just have to keep a tally of the total size of all queued files.

Then in uploadError make sure you remove the total. You'll probably need to track the current uploaded total so you can remove that.

Then in the uploadProgress event sum up the totalBytesLoaded.

I'd store all these variables in the customSettings object.