Why am I forced to format the hard drive in the UDI wizard?

We are using SCCM 2012 SP1 + MDT 2012 Update 1.

I am trying to get a UDI task sequence going for our server admins.  The problem is that they want to be able to create their own partitions and choose which partition to apply the OS. So before the UDI wizard runs we can create our own partitions using DISKPART, but then on the Volume page for the UDI wizard, we are forced to check the box labeled 'Partition and format disk 0.'

This will wipe out our custom partitions. How can UDI just allow me to proceed with my own partitions and apply the OS to the partition I chose in the wizard and leave the rest of the disk alone?