using web config key value in rdlc report

See more:

C#

ASP.NET

RDLC

Hi I have a rdlc report that shows image and image is contained in images folder inside the solution folder. Now i have used external image to show that image and used expression like

="http://localhost/projectname/images/1.jpg"

Its running fine when i deploy published code on iis

But now i want to set servername in web config like
<add key="servername" value="http://localhost/projectname/images/1.jpg">
so that any one can chnge setting in web config and use rdlc
but now i am using custom code to access value of web config my custom code is

Public Function GetUrl() as String

Dim rootWebConfig1 As System.Configuration.Configuration
rootWebConfig1 = System.Web.Configuration.WebConfigurationManager.OpenWebConfiguration(Nothing)
 Dim customSetting As System.Configuration.KeyValueConfigurationElement
    customSetting = rootWebConfig1.AppSettings.Settings("servername")

Return   customSetting.Value.ToString()

End Function

I have also used Reference to System.Web and System.Configuration in rdlc
Now i am seeting value of external image like=
Code.GetUrl()
but image is not showing up
i have taken help of article
http://forums.asp.net/t/1085817.aspx/1[^]
please tel me how to use web config key in rdlc report.