I don't know of a way to suppress it.  My gut says (I admit that I can't find anything authoritative on this) that you can't suppress data on an authorization form that you have the client sign.

The IRS website has a means by which you can monitor the volume of your EFIN usage to make sure it's not being used by someone else.

https://www.irs.gov/tax-professionals/how-to-maintain-monitor-and-protect-your-efin

https://www.irs.gov/e-file-providers/faqs-about-electronic-filing-identification-numbers-efin

I would also say that if I had a client that I suspected might do something like this, I'd disengage anyway.

I'm sorry not to have a more concrete answer for you.