a phone call asking for you at the bank, with some innocuous excuse like confirming a doctor's appt.  When they are switched to your desk, often times they will simply hang up before you answer.  She now knows that you do in fact work there, and that you are not likely LEO, which is all she wants to know.

Swim

I too work in a very sensitive profession and was verified through P411.  They called my place of employment to verify my identity and were very professional and discrete.  In order to avoid any problems here is what I did: when I gave my place of employment info., I provided them y workplace phone number with my extension.  The reps from P411 called while I was out and left a very professional message on my voice mail with a return number.  I called back and they quickly verified my job info.  They never spoke to anyone else at my place of employment.  Hope this info is helpful.

Just be very clear about what script you want them to use and the time when they should call.

However I find that email is much safer than phone calls. Many large firms make it their biz to figure out exactly who's calling and can probably identify most incoming calls , even if the caller has a blocked number. Not every provider uses a throw away cell...hint many have iPhones. So you can set up a brand new dummy webmail account and send a message there from your work account. Just forward the provider the log in details for the dummy account and she can check it at her leisure. The upside is there is no direct link between you and the provider.