[tzs]

Assumption #1: he has an internet connection of his own, using the typical cable/dsl modem => home router => his computer(s) setup.

Assumption #2: there is porn that is not to his taste and he really would prefer not to see.

Fun solution: convince him to give you unsupervised access to his computer and network so you can (you tell him) install filtering software. Tell him you want unsupervised access so that he won't see exactly what you install, so it will be harder for him to disable it.

You then in fact install filtering software on his computer. No doubt he'll find this and easily bypass it. That's OK, because during your unsupervised access you ALSO install custom firmware on his router.

This custom firmware looks for porn, but does not block it. Instead, it randomly replaces a small fraction of the images with images of porn your friend finds disgusting. For instance, if his interest is straight porn with no kinks, get images from some fetish site that features naked fat men defecting on masturbating barely legal boys, or something worse. Go wild here.

This should greatly reduce his interest in porn sites (or greatly broaden his tastes...so I guess there is some risk!).