Select disk layout during the task sequence

Hello,

I was hoping someone out there might shed some light on this. I've been trying to figure out a way to select my OS disk layout during the task sequence. For example, I'd like to prompt for the percentage of the disk to use for the OS partition. I have an HTA that I use to prompt for some other information (like the computer name, operating system, etc.). I was hoping to just modify the OSDPartitions0Size task sequence variable in my HTA at the same time but that won't work. The "Format and Partition Disk" task always runs before the HTA (presumably so it has a place to store the packages).

Any feedback is appreciated!