What you're proposing is basically the same as a notice period (at least in the UK), and neglects that it's still high risk for the candidate. To be able to come in and work for a month they have to leave their existing job. I'd have to be pretty damn sure I'd have no difficulty passing my probation in order to risk being out of work.
It's high risk for currently employed candidates, yes. I hadn't considered that mainly because my company's main source of candidates is unemployed college graduates.
