Thanks for writing in! Regretfully this isn’t a feature offered by X. It could be possible with custom development, but this would be outside the scope of support we can offer. You may wish to consult a developer to assist you with this. X is quite extensible with child themes, so there are plenty of possibilities.
What you can do is to make your custom element in Cornerstone and add the attribute to the element:
Thanks for understanding. Take care!