carrie..
Sure Carrie, giving someone a gift of any kind is a wonderful feeling and being generous is a good thing, especially when it is for someone in need. However giving because it feels right to do is a whole lot different then giving because you have been sent a request in the mail!
Mrs.J you seem to be using your instinct when you questioned this and you are right, there is no easy way to ask for something. The best way out of this is to plan a fun baby shower, do not register anywhere, and know you are going to host a great time.
Most people go to a baby shower with a gift (it is never to be expected, that is just rude). Often people will ask the host if they know what the new mommy needs. chances are close family will just ask her directly. If someone asks you, you could just say, I think gift cards and cash are what she needs the most, but she will be happy you just come!
It is really not nice to ruin an invitation with a gift request included, its 100% tacky.