<?php

function assign_to_array(&$array, &$keys, $value)
{
  foreach($keys as $key => $val)
  {
    if (count($keys) == 1)
    {
      $array[$val] = $value;
      return;
    }
    else
    {
      array_shift($keys);
      if (!is_array($array[$val]))
      {
        $array[$val] = array();
      }
      $a = &$array[$val];
      assign_to_array($a, $keys, &$value);
    }
  }
}

$array = array(1, 2, 3);
$keys = array('a', 'b', 'c');
assign_to_array($array, $keys, 'someValue');
var_dump($array);
?>