One way would be to serialize the array, define the serialized variable as a constant, then unserialize it when needed. (A defined constant is global.)
Another, probably better, way to do it would be to pass the array by reference to the function.
Edit: reference example:
function test(&$arr)
{
$arr = array('abc', 'def', 'ghi');
return true;
}
test($my_array);
print_r($my_array);