ext_tables.php

$pluginSignature = str_replace('_','',$_EXTKEY) . '_list';
$TCA['tt_content']['types']['list']['subtypes_addlist'][$pluginSignature] = 'pi_flexform';
t3lib_extMgm::addPiFlexFormValue($pluginSignature, 'FILE:EXT:' . $_EXTKEY . '/Configuration/FlexForms/flexform_list.xml');

gistfile1.txt

<T3DataStructure>
  <sheets>
		<sDEF>
			<ROOT>
				<TCEforms>
					<sheetTitle>Algemeen</sheetTitle>
				</TCEforms>
				<type>array</type>
				<el>
					<switchableControllerActions>
						<TCEforms>
							<label>Selecteer type</label>
							<onChange>reload</onChange>
							<config>
								<type>select</type>
								<items>
									<numIndex index="0">
										<numIndex index="0">Laatste berichten</numIndex>
										<numIndex index="1">News->latest</numIndex>
									</numIndex>
									<numIndex index="1">
										<numIndex index="0">Lijst</numIndex>
										<numIndex index="1">News->list</numIndex>
									</numIndex>
									<numIndex index="2">
										<numIndex index="0">Meest populair</numIndex>
										<numIndex index="1">News->mostPopular</numIndex>
									</numIndex>
									<numIndex index="3">
										<numIndex index="0">Producten lijst</numIndex>
										<numIndex index="1">Product->list</numIndex>
									</numIndex>
									<numIndex index="4">
										<numIndex index="0">Evenementen lijst</numIndex>
										<numIndex index="1">Event->list</numIndex>
									</numIndex>
									<numIndex index="5">
										<numIndex index="0">Trainingen lijst</numIndex>
										<numIndex index="1">Training->list</numIndex>
									</numIndex>
								</items>
							</config>
						</TCEforms>
					</switchableControllerActions>
					<settings.foo>
						<TCEforms>
							<label>Foo</label>
							<config>
								<type>input</type>
							</config>
						</TCEforms>
					</settings.foo>
				</el>
			</ROOT>
		</sDEF>
	</sheets>
</T3DataStructure>