Hi John,

In a modal dialog we have two formats : Fixed size and Standard (Expandable). If you use Standard then you can increase the size of the modal dialog at runtime. But adding a maximize icon is not possible as the intention of Modal dialog is to "Users cannot continue with other work until submitting the form or dismissing the modal dialog box". 

Instead of modal dialog you can use a Pop-up window to get the maximize icon.

Regards,
Evita.