Hi NeilA,
I have never tried that, but it seems it should be possible to put featured items in a module, but then restrict virtuemart to registered users.
You might be able to use {loadpostition} or {loadmodule} to place the featured products module into an article. Then when they click through they will be asked to register before they can view the store.
www.ostraining.com/blog/joomla/loadposition-loadmodule/ You can also make products visible by creating user groups in the Virtuemart admin. Then assigning access to the products by group.
Give us some more details on what you are trying to accomplish. We might be able to suggest something more specific.
Cheers,
Ed