Humble Bundle question.

You don't need to register to get Tropico ... and no there is not

Nope.

He doesn't need to be registered to humble bundle to redeem the link. He can just link his steam account to the particular humble bundle page.

You don't have to make an account to link it to your steam. Creating an account will just let you claim the page.

with the new system? nope.

Aw damn, He won't link his account eiter. Ah well, thanks anyway.
Some left over Reciever. One might be used I forgot.
https://www.humblebundle.com/?gift=sb2ZT75YrED2xTMB
https://www.humblebundle.com/?gift=PBz3Azwqz3uTYuAy
https://www.humblebundle.com/?gift=X5fbnfvaunDvHPww
https://www.humblebundle.com/?gift=xxmzArFT6HUErW4m
https://www.humblebundle.com/?gift=zdywCBmaVvTvFmyq

well, there are one-time-email-adresses for that purpose

Tell him to go to https://www.hushmail.com/ Create a new account for this purpose, then leave the account alone. If you don't log in at least once for 7 days in a row, the account gets deleted. No mess, no fuss