Is there a Prompt or Interactive Message Box available in a server-side script?

I know that from a User Defined Script or a Customizer script that runs on the server, you can display a message box thusly:

retval = oSession.AsObject(oSession.UI).MessageBox("Hello World?")

However, I need to throw up a message box that prompts the user to click OK or Cancel, or Yes or No, and then have my code take a different path depending on what they choose.

This is possible with vanilla VB Script, which means it's possible with a customizer script that runs on the client. However, I need to be able to iterate through the lines of a current invoice (i.e. before it has been written to disk), and if I find a particular item code in a line, throw up a message box asking if they want to do an action, in this case add a handling charge.

Because the script needs to see the current lines in memory, it makes sense to have it run on the server. Also, it will need to update the lines grid when the script is done, which is really only possible with the oScript.LoadGrid() method.

Thanks.

Aaron