Who am I to say that your client wouldn't be flattered and would jump at the chance?  Or wouldn't run screaming into the night never to be heard from again? ¿QUIÉN SABE?

At least you are planning on obtaining consent - rather than collecting a specimen, tossing it in the freezer and using a turkey baster later at your convenience... and then pursuing Daddy for child support.

Hope I haven't given you any ideas...

Guys - if you aren't planning on reproducing - you might want to get fixed.  Some forms of VD are pretty curable; children not so much...

But there is a potential hazard to the donor. If after the baby was born the woman might try claim child support, accuse the donor of rape,  or any of many extortion schemes. With donor's DNA as evidence I would think that she would have a strong case . Granted, I'm no lawyer but it was a thought. Again, I'm not suggesting that you are anything but SINCERE.

Don't say it's for you, but tell him it's a "just in case" kind of thing should he later on regret the decision.  Perhaps you've heard tale of others who later wished they had taken this step.

Then if you both agree later on, the sample can be released to you with whatever contracts the pair of you deem appropriate.

http://www.early-pregnancy-tests.com/semen-collection-condom.html