Microsoft allowed to build Bootable USB Drive with Hyper-V Server 2008 R2 on it.
Here is an official manual how to do that: USB creation process detailed.
You can download a GUI that should simplify the creation process from MSDN web site, but for whatever reason this GUI doesn’t work for me (I spend a lot of hours on it. Maybe it’ll work for you).
So, because I had problems with this GUI, I decided to build my own automotive process :). I’ve built a script that does all steps from official MS document and compiled it into EXE file.
More details here: http://www.itstuff.ca/2009/12/create-bootable-usb-drive-for-hyper-v.html