How to add "Authorization" header under HTTP Header Manager

Hi,

My HTTP service overrides the "Authorization" header and provide a
signature string value to the Authorization header.
Now I understands that JMeter omits this header if added under HTTP Header
manager. Instead we should use HTTP authorization manager.

But I can not use HTTP Authorization manager since it's not a user/password
thing. Is there any way to control Jmeter such that it doesn't omit the
Authorization header under HTTP Header manager?

Thanks,
Pradeep