When I originally wrote this post, there was almost no information available for running HP Image Assistant during an OSD task sequence. Thankfully, that is no longer the case. However you ended up here, I'm going to do you a favor and point you to a newer blog post that does a far better job than I did.
Apply Firmware and Driver Updates Using HP Image Assistant by Ryan Engstrom. Ryan has documented not just the basic approach that I had included here but also some more advanced variations.
I'm currently working on a custom PowerShell WPF app utilizing HPIA, HP's Client Management Script Library and an internal collaborative storage solution. Here's the first entry in that blog series, in case you're intrigued: https://adminsccm.com/2019/05/29/hp-drivers-in-a-world-without-maintenance-windows-part-1/