I think the only way to do this is to set the attribute value in javascript. I just saw a new widget in the appstore that might be of some help.
https://appstore.home.mendix.com/link/app/111554/Mendix/Attribute-Helper
Hi Ockert,
Could you maybe share your page extender solution with me? I am having the same challange as you.
Please let me know.
Kind regards,
Jeroen