SSL + Domain Mapping - Only for Main Site

I have a multisite network with the following attributes:

- subdomain install
- WPMUDEV's Domain Mapping plugin
- Wildcard SSL cert

For now, I only plan to accept payments on the main site. I purchased the Wildcard SSL in case I want SSL on any of the subdomains down the road.

How do I go about adding SSL to specific pages (i.e. payment and login) on the main site?