To configure a default server variables, navigate to Administration > System Options > Dynamic Site Server > Server Variables. Then click Default Variables. 

Select variables from the list that you want to include in a page's IGX_Info element when a page is rendered in preview. To find out more about individual IIS server variables and their functions, see this MSDN article. 

To add a custom server variable, navigate to Administration > System Options > Dynamic Site Server > Server Variables. Then click Custom Variables. (Note that these variables must first be configured in IIS.)

Click New. Enter the name of the variable(s) you want to add. Then click Save.