检索动态子阵列

I'm trying to create a mail form customizer but now I'm stuck about creating dynamic keys to be used as checkbox fields.

My example PHP file:

$name = 'Jonh';
$userKey = 'SomeKey';
$userValue = 'SomeValue';
$customArray1 = 'SomeKey';
$customArray2 = 'SomeKey';
$customSubArray1 = array(1,2,3);
$customSubArray2 = array('apple','orange');

$array = array (
    'Name'                  =>      $name, 
    $userKey                =>      $userValue,
    $customArray1           =>      $customSubArray1,
    $customArray2           =>      $customSubArray2
);

I can get those values and keys using foreach to be sent by mail using phpmailer class:

$row = '';
foreach ($array as $key => $value) {
   $row .= "$key"." - "."$value";
}
echo $row;

Then the PHP show:

Name Jonh UserKey UserValue Array Array

I'm retrieving data submited by the user from a database. How can I let the user create the any keys and values as they want and retrieve it? These keys must be string or child array.