Releasing Subsitute Part to a Job


We manufacture our own computers for our end product. My question is:
We have released a job to build 50 computers, we purchase a Western
Digitial Drive(on the BOM), with a IBM Hard Drive as a sub. part(Not on
the BOM). I have 45 WD Hard Drives in stock which I can release to
manufacturing, and I want to use 5 IBM Hard drive to complete this job.

How do I release them to the job?? This is probally something stupid I
am missing but. . . .