Any way to prevent one user from changing his password?

Hey everyone. I run a WordPress-based membership site. With the plugin I’m using (Wishlist Member) users automatically register themselves.

I want to manually set up one account for “trial” access, though, that is given to all non-customers to see what I have to offer. I will manually set up this account and set its password. I want to make it so no one can change the password on that single user. There is an option to make it so no one can change their password, but I don’t want to prevent existing users from being able to do this.

Is there any way to “lock” only this user account so that the password cannot be changed?