...
<el>
   <vereinuid>
      <tceforms>
         <label>
            LLL:EXT:svd_league_fe/locallang_db.xml:pi1_flexform.vereinUID
         </label>
         <config>
           <type>group</type>
           <internal_type>db</internal_type>
           <allowed>tx_cfcleague_teams</allowed>
           <prepend_tname>0</prepend_tname>
           <minitems>1</minitems>
           <maxitems>1</maxitems>
           <size>1</size>
         </config>
       </tceforms>
      </vereinuid>
</el>
...

protected function init(){
    $this->pi_initPIflexForm();
    $this->pi_loadLL();
 
    //Verein holen
    $this->conf['vereinUID']=
       intval($this->fetchConfigurationValue('vereinUID'));
 
    //Template holen
    $this->conf['templateFile']=
       intval($this->fetchConfigurationValue('templateFile'));
...
 
protected function fetchConfigurationValue($param) {
   $value = 
       trim($this->pi_getFFvalue($this->cObj->data['pi_flexform'], $param));
   return $value ? $value : $this->conf[$param];
}

$TCA['tt_content']['types']['list']['subtypes_addlist'][$_EXTKEY.'_pi1']='pi_flexform';
 
t3lib_extMgm::addPiFlexFormValue($_EXTKEY . '_pi1','FILE:EXT:' . $_EXTKEY . '/pi1/flexform_ds.xml');