Microsoft has released hotfixes that now add 802.1x support to both WinPE 2.1 and WinPE 3.0. Here are the links to the hotfixes.
WinPE 2.1: http://support.microsoft.com/kb/975483
WinPE 3.0 (Windows 7 & Server 2008 R2): http://support.microsoft.com/kb/972831
Step by Step Instructions to Inject the update using DISM.
1) Once you have downloaded the update, extract the files to your deployment server. In this example, I created a folder on my E:\ called 802PE.
2) Mount the LiteTouchPE_x86.wim using DISM: DISM /Mount-WIM /WIMFile:E:\DeploymentShare$\Boot\LiteTouchPE_x86.WIM /index:1 /MountDir:E:\Mount
3) Inject the package: DISM /Image:E:\Mount /LogPath:AddPackage.log /Add-Package /PackagePath:E:\802PE\Windows6.1-KB972831-x86.cab
4) Unmount and Commit your changes: DISM /Unmount-WIM /Commit /MountDir:E:\Mount
5) As an additional step you can validate the package was installed successfully: DISM /Image:E:\Mount /Get-Packages (Note: When you add the package in step 3 it should tell you, “The operation completed successfully” if the package injected with no errors.)