I'm just a cynical colonist, but I can't help thinking that an employer asking for that form prior to giving you a job offer is just borrowing the implied authority of government to convince you to compromise your own negotiating position. There absolutely is a point to concealing your previous salary until after they give you a job offer with defined terms. If they learn your salary history subsequent to that, it won't cause them to suddenly renegotiate your compensation package.

So yes, find a different excuse, but find an excuse.