have tp available and don't bring it up unless they ask or things get really serious. if he's ok enough w all the other crunchy behaviors to get serious in the first place, he'll already be in far enough to either deal with or get on board with family cloth.
i don't use anything disposable, if i can help it. this is what i tell people. if they need specifics i discuss it openly as if i were talking about the weather - how will this stuff ever be considered normal if we can't even talk about it normally? so sure, people find it odd, but who cares? the trees love me.
I would have environmentally friendly tp available for the first few times that your dates come to your house, and just wait until it is brought up naturally in conversations, like when you are telling your date how important the environment is and how you have made changes in your own lifestyle to try to make as little impact on our environment as possible.