Every time someone posts a "trick the IRS computer" procedure, I have to disagree because doubling the gross income on a return is also likely to double the likelihood of an audit.  

Or maybe it will quadruple the likelihood of an audit.  Or maybe it makes no difference.  I'm just not going to sign a return that says a client is self-employed, when he isn't, and in fact is arguing against it elsewhere. 

But what's important here is that there are many hoops to jump through to qualify for 1402(k).  Insurance companies have an army of lawyers and accountants to make sure they don't get in trouble with IRS.  Your client doesn't.  He only has you, and the least you (or your client) should do is ask the company for documentation of why they are using the 1099-NEC.