I first built a function to loop through the number of times you want to clone your element .. And I made a function that will insert the clone after the desired key ..  It's an amalgamation of two functions I had already built for different purposes ..
<?php
$array = array();
$array[0] = 'Clone Me Please';
$array[1] = 'Clone Me Too Please';
$array[2] = 'I am here for decoration';
print_r ( cloneItem(0,$array,3) );
print_r ( cloneItem(1,$array,2) );
function cloneItem($itemKey, $array, $timesToDuplicate){
        $clone_me[0] = $array[$itemKey];
        for ($x = 1; $x <= $timesToDuplicate; $x++){
                $array = array_insert_after($array,$itemKey,$clone_me);
        }
        return $array;
}
function array_insert_after( $array, $key, $new ) {
        $keys = array_keys( $array );
        $index = array_search( $key, $keys );
        $pos = false === $index ? count( $array ) : $index + 1;
        return array_merge( array_slice( $array, 0, $pos ), $new, array_slice( $array, $pos ) );
}
Output ..
Array
(
    [0] => Clone Me Please
    [1] => Clone Me Please
    [2] => Clone Me Please
    [3] => Clone Me Please
    [4] => Clone Me Too Please
    [5] => I am here for decoration
)
Array
(
    [0] => Clone Me Please
    [1] => Clone Me Too Please
    [2] => Clone Me Too Please
    [3] => Clone Me Too Please
    [4] => I am here for decoration
)