Remove disabled attribute/state during submission
Once you submit a form, you are not able to retrieve disabled inputs (https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#constructing-the-form-data-set). That said:


You cannot modify input's attributes from server-side since the submission data is already posted.
Developing your solution with jQuery on .submit() function is a good idea (far away from bad practices).
You can also make another work around: instead of disabling you could use readonly="readonly" attribute (https://www.w3.org/TR/REC-html40-971218/interact/forms.html#h-17.12.2)