How can I format a Data Item String

[blindz]

So I have a text field that I am calling in a Data Item from a DB list. I am trying to format this field so it only shows the last 3 digits of the passport number and then mask the first 6 with # signs. How can I do this inline or do I have to go to the code behind?\[code\]<asp:TextBox ID="txtPassportNumber" runat="server" MaxLength="9" text="<%# ((TSAPassenger) Container.DataItem).Passport.DocumentNumber %>" Enabled="<%# IsOutsideTenDayCutoff %>"></asp:TextBox>\[/code\]