Microsoft Deployment Toolkit: Add/Remove WinPE Boot.wim Files To A USB Flash Drive Tool
From the archive (2010). Written for the tools of the time, so some details may be out of date.
Keith over at Xtreme Consulting has created a nice wizard driven tool for adding boot images to a USB flash drive. This is designed to work with MDT 2010.
Read the full post and download the tool here.
Excellent work Keith!