You could either have a model binder that does a split (like Peter mentioned), or you could use JavaScript to add hidden fields with the same name for all the values. Something like:
<input type="hidden" name="customers" value="102" />
<input type="hidden" name="customers" value="123" />
<input type="hidden" name="customers" value="187" />
<input type="hidden" name="customers" value="298" />
<input type="hidden" name="customers" value="456" />
Then your action would take the enumerable of int like:
public ActionResult DoSomethingWithCustomers(IEnumerable<int> customers){....}