The alanabit/McGrath idea makes no sense to me and is I think impractical. Here's why:

If I* was one of several men having slept with a woman who became pregnant and she'd choose me as the "father" what would stop me from saying she has only invented our making love for the sake of my better job than the other guys. Usually man and woman are alone and without witnesses when they make love. It would be her word against mine and since she has a lot to win her motives may be in doubt. Any judge would opt for a paternity test and this way I'd get what I did wanted in the first place: a chance not to pay. That's why this idea never can work.

I*: not me personally. I've longed to be a father for so long that I'd been glad about any such offer to play "father".

Wolfgang