SomeModelAdmin.php

<?php

class SomeModelAdmin extends ModelAdmin {

	private static $managed_models = array(
		"MyDataObject"
	);

	public function getEditForm($id = null, $fields = null) {
		$form = parent::getEditForm($id, $fields);

		$gridField = $form->Fields()->dataFieldByName('MyDataObject');
		$detailForm = $gridField->getConfig()->getComponentByType('GridFieldDetailForm');
		
		$detailForm->setItemEditFormCallback(function($form) use ($self) {
			// You can use $form in here
		});

		return $form;
	}

}

This morning I get a different idea. Since I only wanted to add extra class on form, I actually get the Tab that I'm on and add class there. It work like a charm, so no need to wrap fields or doing anything. Thank you for your help btw.