Membership 2 Pro - partial registration woes

So...

The issue I have is really about stopping sneaky sneaky people from semi-completing the membership registration process to see semi protected content.

I have sent up the paywithalike plugin to show a 'like' message if people aren't members of my site (or more correctly to not show the PWAL message if they are 'subscribers').

The PWAL message I use suggests people become members to avoid seeing the 'like-wall' and (yada yada) support the site.

People then register for an account to start the membership process but then skip the lovely paying bit. However they now have site account so can happily skip my 'like-wall' and I end up with no likes and no money.

Ideally then, people only become 'subscribers' if they've completed paying for a modestly priced membership (we use mailchimp for our newsletter so don't need subscribers per se).

There might be a better way of achieving what we're after or even some tweak we missed any help much appreciated.

A