Are you using AHCI? And do you have WHS Power Pack 1 installed?
I eventually got rid of my WHS system, I found it too limiting, but I thought you could do this by using the Restore CD. If you don't know where it I think it is available on your network via \\<WHS>\Software\Home PC Restore CD\
What makes you say it is better to be the system partition on a larger disk? Hardware specifications aside, a hard drive’s size has very little to do with its performance, unless the drive is almost full. For optimum performance NTFS requires a between a minimal of 10-15% of the hard drive to be free space.
.:: Vista Ultimate x64 :: Antec Fusion :: Corsair HX520w :: ASUS P5E-VM :: Core2 Duo E8400 3.0Ghz :: 4GB RAM :: 128GB SSD System\Apps :: 1TB\5TB Data :: LG GGC-H20L BD/HD DVD :: HDHomeRun x2 ::.