We can add below tag under ConfigSections

<section name="infragistics.web" type="System.Configuration.SingleTagSectionHandler,System, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>

and set directory paths using below tag after </configSections> as shown below:

<infragistics.web imageDirectory="../ig_common/Image" javaScriptDirectory="../scripts" cssDirectory="~/css" formsDirectory="~/forms"/>