You need to lean on the hiring manager and tell him to make them stop. He wants you, but HR is HR and they have their own processes. They are also used to being in control and having the upper hand in any negotiations. It's possible he has no control, but every place I've worked, the hiring manager can absolutely put the brakes on the BS and go directly to an offer. It's his call.

If the HR department is really that powerful and obnoxious, maybe you don't actually want to work there after all. A crap HR department can be an ongoing headache.