Initially, I was tempted to say "registry with U.S. Wellness, Tropical Traditions, etc. - and people will get the hint."
But then I remember what all the advice columnists say about specifying gifts you want for showers, weddings, etc. In one word: Don't. It's plain bad manners. Registry information isn't supposed to be included on the invitation card. Asking for cash instead is the height of tackiness/rudeness.
Maybe the real question here should be: Are shower gifts Paleo? :-)
Honestly, just let the guests give what they want to give. If they ask for gift ideas, though, then you have full leeway in saying exactly what the mother-to-be wants.
These are examples from a Carolyn Hax chat (for a wedding shower, but the same applies to all showers), here: http://www.washingtonpost.com/wp-dyn/content/discussion/2010/06/04/DI2010060403694.html
Bethesda, Md.: I received a wedding invitation recently that had "Monetary gifts preferred" written on the bottom in big letters. No question, just wanted to let everyone know that the apocalypse is nigh.
Carolyn Hax: Eh, that particular harbinger announced itself years ago, and we're all still here, more or less.
Hope you sent regrets. That's really the best weapon against the trend--especially since all the yowling we do about it in this forum doesn't seem to have made a dent.
D.C. Area: My soon-to-be-married son mentioned they would like to receive monetary gifts toward a honeymoon. I told him it was absolutely unacceptable to put that on any type of invitation. However, I have heard of a "honeymoon registry" (I have not mentioned that to him yet - I want to check it out more before putting that but in his ear). Is it acceptable to add include a "honeymoon registry" with the standard department store registries so guests have more options?
Carolyn Hax: It is absolutely unacceptable to put any registry information in with an invitation. Registries exist not for the enrichment of the couple, but solely for the convenience of the guests, who might prefer to give stuff vs cash, but who don't want to spend their cash on stuff the couple doesn't want. This information should be provided (by the bride, groom or family/close friends of) solely upon request.
It is a really, really narrow set of parameters, and, full disclosure, I don't even like those any more. I used to feel pretty neutral about registries (keep em out of the invitations, but otherwise go for it--I even had one myself), but now--after years of reading about and witnessing their abuse--I wish they'd just disappear. If you don't know what the couple wants, write a check. With that one sentence, all registry justifications go away. Now if only the registries themselves would go away ...
Oh right, you had a question. If he and his intended -need- some things, then they can put them on a regular registry. It is not cool to ask the guests to send them on a honeymoon. If you get asked by close friends what the couple would like, you can use your judgment on saying, "Cash always fits." Really--it has to be people you trust not to find that offensive.