Then the candidate says something like "Well, you know, I can't take any payment before I'm out of this job. Can't I just do it for "free", and payment come as a bonus on hiring?"
It's a risk you take, or don't, it'll certainly depend on how compelling is the job.
But you are the one that placed yourself in a bad situation. They have a sane procedure that fully respects you, but isn't fine-tuned to your current problems. You can try negotiating their procedure too, but in their place (what I'm not, I'm in the "can't bill you" place right now), I'd refuse to.