Add items Permission level

Hi, 

I'd like to know a way to set permissions on a list so that users in the SharePoint site - Members group can't see existing items in the list that don't have unique permissions assigned. They can only add new items in this list. Once an item is created, a workflow would be triggered that would add a unique permission only for that item.

The problem is that when creating a Permission Level with only the ability to add items, the user loses access to the custom item creation form.