[TYPO3] Add configuration field in fe plugin

[Juan Madurga]

Hello,
Im extending an extension and i want to add a new configuration field not 
store in the DB.
I have written in ext_tables.php this:
$tempColumns2 = Array (
	"tx_extensionextend_owners" => Array (
		"exclude" => 0,
		"label" => 
"LLL:EXT:extension_extend/locallang_db.php:tt_content.tx_extensionextend_owners",
		"config" => Array (
			"type" => "select",
			"foreign_table" => "fe_groups",
			"foreign_table_where" => "ORDER BY fe_groups.uid",
			"size" => 5,
			"minitems" => 0,
			"maxitems" => 100,
		)
	),
);

t3lib_div::loadTCA("tt_content");
t3lib_extMgm::addTCAcolumns("tt_content",$tempColumns2,1);

Doesnt work.I have debugged and i only have the [data] varibles of the 
original extension- Whats the problem? I also have tried with flexforms but 
the same result, nothing.
Please Help me

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