Digi has already provided instructions on how to do this. It is only possible to do after running Bart's PE once. When you run it do not have it create an ISO. Then you will replace files in the "PEBuilder" folder. Then manually create the ISO image. I will find the post, it provides all the instructions.
It could be an "illegal" hack to change the boot screen according to M$, and the only way to do it is after running PE Builder. So I cannot include it in the project. However, the instructions are in the forum and I cannot stop whatever any of my users want to do.

Here is the link to the topic:
http://www.ubcd4win.com/forum/index.php?showtopic=1081&hl=screen