Membership 2 on multisite handle new users

I have a multisite and each blog is using Membership 2. But the registration isn't very smooth for users who already registered on another blog. For example… A users registers on and then finds and decides to register… They get an error that someone with their email is already registered… They think… "No I didn't…" How can we make this smoother. Can't we just add that user to the blog instead of giving an error?