Pass data to hook_entity_insert
Since you're not initiating the hook, you'll have to find another way. Maybe call a hook in the hook you're implementing?

If you would've been initiating the hook, you could've just passed on more parameters and used func_get_args to get the parameters, ie:

function sum ($a, $b) {
  $sum = 0;
  foreach (func_get_args() as $arg) {
    $sum += $arg;
  }
}


and call it with

sum(1, 2, 3, 4)