My experience as a hired expert with QS-9000 and TS 16949 audits has been that you need to consider the intent of the restriction that consultants can be present only as observers.
Fortunately, I must endorse the good judgement of the vast majority of registrar personnel who have been auditing my clients.
The origin of this requirement was the tendency in the early days for companies to hire a golden-tongued scalawag to sweet talk the auditor, telling him or her what they wanted to hear... regardless of actual practice. Another frequent failure mode was that the consultant disappeared once the certificate was completed.
However, when a client paid my organization fees to have me on site full time for six months to develop a system, I believe that we were certainly not in
this position, but were a bona fide part of the organization.
In order to provide the registrars clarity on this point, we made it clear that I was not a "consultant", but rather a contract employee --
-- Training records and qualifications in the employee files with other temps
-- Place on the org chart, called out as a contract employee
-- a well defined set of responsibilities (many) and authority (little!)
Additionally, in the course of the audit, I would limit my involvement to that
of guide and quality system expert. If the auditor wanted to see compliance,
I would take them to the appropriate employee doing the job, introduce them,
and keep my mouth shut. (Those who knew me personally realized how
difficult this was for me!!!

On the other hand, if a question came up regarding how the system met the standard, I could and did speak up and
explain the logic. Similarly, if I had done the internal audit, I was subject
to being audited directly on that topic.
Good auditors treated this the same way they would treat a manager/guide.
They might ask the manager/guide a question... but they'd also ask the
employee actually doing the job. If necessary, they counsel the guide to
remain silent and let the employee answer. It's no different.
Best regards........................Brad