Using the “Captcha”-like page before WP Login for one other page possible?

Dear NinTechNet team,

first of all: Thank you for such a helpful tool to minimize risks.

My question is:
Is there a way to use the Captcha-like page that is shown before you actually log in to the WP Dashboard with your credentials for one other page, too?

The background is as follows:
I’m planning to add a community/forum that does not use the internal WP registration, but it’s own. The registration however adds user accounts in WordPress, it’s just that it uses its own form and system for that.
To prevent spambots from bombarding the form and (ab-)using random mail addresses, I would like to call that Captcha-esque page that gets called before you can actually enter your credentials in the WP Login form (wp-login.php).

Best regards
Ronny.