It is possible to apply the OS to disk one with some workarounds, we instruct our engineers to diasble sata 0 and 1 before a build and we have a dell bios exe in the task sequence to switch sata 0 and 1 back on later in the TS after the image apply section, we also run bcdedit commands to fix the boot manager, a further VB script sorts out the drive letters as we prefer the second drive as D: but that is niether here nor there. Works on M6800 and M4800's.
We are also working on the Dell CCTK commands to do this automatically without any manual intervention, but I'm struggling with the flakey way this happens in WinPE.