How do I change the login/register/account buttons in the sticky bar to point to a custom page of my choosing?

You can manually set what you want those URLs to be by editing the inc/sticky.php file. There are five lines you must modify. First, change line 93 and make it equal your desired account URL:

$hrefaccount = force_ssl_admin() ? str_replace('http://','https://',admin_url( 'profile.php' )) : admin_url( 'profile.php' );

Change it like so:

$hrefaccount = 'href="http://www.youraccounturl.com"';

Then change lines 92 and 103 to match your desired register and login URLs respectively:

$hrefregister = '';

...

$hreflogin = '';

Like this instead:

$hrefregister = 'href="http://www.yourregisterurl.com"';

...

$hreflogin = 'href="http://www.yourloginurl.com"';

And finally change lines 91 and 102 from:

$idregister = 'sticky-register';

...

$idlogin = 'sticky-login';

To this:

$idregister = 'sticky-register-custom';

...

$idlogin = 'sticky-login-custom';