Turn the tables and imagine getting an invitation to a virtual shower yourself.
"You are not invited to a shower, but Stephanie is pregnant and is registered at Target, Babies R Us, and Amazon. By dr's orders, she cannot fly after 25 weeks, so she does not want to see you near her home town, has no intentions flying before 25 weeks, and does not want visitors until after the baby is born. So please send a gift by the due date because this is her first and she needs a lot of baby stuff that she doesn't want to buy. Please spend your hard earned money on Stephanie without enjoying her company for the afternoon at a shower."
That is what I'd read if I received an non-invite like that. If people want to send gifts, they will. But we live in such a gift-grabby society, that people would really be offended if they received that type of announcement without even the exchange of a gift for a piece of cake and getting to ohhh and ahhh over baby stuff.