10
As I see it, you have three options:
1. disable registrations completely
2. Allow registrations but set the system to "Admin Activation", thereby giving you control of things
3. Edit that template as advised (not too difficult) and, to be sure, rename register.php to fool the smartar$es
From what you say, either of 2 or 3 would do; just make your choice of which suits you best.