Hi Enrique,
I have only just got around to testing the code that you posted and it does exactly what I was asking about. It is certainly far more elegant than the method I tried a while before to create something like this.
There is a minor issue that I think may be relatively easy to resolve though.
The plugin appears to not be aware of any advanced grading that is taking place, such as via the new marking grid or rubric. Each of those has an instanceid associated with them that is used in their fillings table {prefix}_gradingform_guide_fillings and {prefix}_gradingform_rubric_fillings. They do seem to remain in the table after an amendment or regrade takes place so it may be just enough to store the instanceid at the time of adding the attempt to history. I would assume the advanced grading would not change between attempts but you might also save the type of advanced grading method used too.
I guess you would also need to display the attempt also but I think this would be a method call using the instanceid.