ssl / https / subdomain for a single page within one WP installation

Hello,

I’m running a WP blog and need a safe form one a single page. I want to protect the page with ssl/https.

My hoster told me, that it’s NOT possible to switch within one domain between http and https. Thus, I want to order the ssl certificate for a subdomain.

At the end, it should look like this:

WP page tree:

/page_1
/page_2
/page_3_ssl_protected
/page_4

URL:

https://www.domain.com/page_1/
https://www.domain.com/page_2/
https://ssl.domain.com/page_3_ssl_protected/
https://www.domain.com/page_4/

How can I tell WordPress to load this single page via https://ssl.domain.com/ instead of https://www.domain.com/

Thanks for your help!!

Lorenz