Still not totally sure what you require but good luck.
if you need an Ajax solution then it can be done with a bit of JavaScript and a call to the "view.html.php" like this:
JS:
var url = "index.php?option=com_demo&view=users&layout=ajax&render=userinfo";
PHP:
protected function displayAjax($tpl = null)
{
$jinput = JFactory::getApplication()->input;
$render = $jinput->get('render', null, 'CMD');
$token = $jinput->get('token', null, 'BASE64');
$values = $jinput->get('values', null, 'ARRAY');
switch($render)
{
case 'userinfo':
$user = JFactory::getUser();
$model = $this->getModel();
$model->setState('filter.user_id', $user->id);
$item = $model->getItems()[0];
echo json_encode($item);
.
.
.
Or the loadFormData Method should allow you to pass the user id in a filter like "&filter_user_id=1" as part of the url
/**
* Method to get the data that should be injected in the form.
*
* @access protected
*
* @return mixed The data for the form.
*/
protected function loadFormData()
{
// Check the session for previously entered form data.
$data = JFactory::getApplication()->getUserState('com_demo.edit.useritem.data', array());
if (empty($data)) {
//Default values shown in the form for new item creation
$data = $this->getItem();
// Prime some default values.
if ($this->getState('useritem.id') == 0)
{
$jinput = JFactory::getApplication()->input;
$data->id = 0;
.
.
.
$data->user_id = $jinput->get('filter_user_id', $this->getState('filter.user_id'), 'INT');
