Trigger Exceptions

Hi everybody. I've run out of knowledge and would love some help.

Our company takes in large orders and sends out smaller chunks of the order over relatively long periods of time. I'm wanting a small dialog box to pop up and remind our administrative people towards the end of the order to contact our customers to request a new purchase order.

I've created a trigger that fires exactly when I want it to fire, however it seems as though I can only use a fatal error. I've tried log, info, notice and warning but none of these pop up a dialog box. The problem with the exception is it aborts the process. Is it possible raise an exception that does not abort the process, or change the client_min_messages to flag notices? If its possible to change client_min_messages I have no idea how and would love some pointers.

Thanks for your help.