Changing http to https automatically

We have an internal multisite/network setup running on SSL (https). When a new user creates a site using our registration page (wp-signup), the page is automatically created using http in the home and siteurl lines, which we then manually have to change to https in the site settings.

Is there any way to get these to automatically create siteurl’s and home url’s from the wp-signup page when the site is created? I’ve looked for plugins, and hard-coding, but as of yet, I’ve not found the command for creating siteurl’s/home url’s.

Thanks everyone!!