Add HREFLANG to the Multisite Sitemaps Plugin

Hi,

I found out that you can add the hreflang tag that Google webmaster tools requests to the sitemap. (https://support.google.com/webmasters/answer/189077) This explains the syntax: https://support.google.com/webmasters/answer/2620865

Is it possible to add the capability to the Multisite Sitemaps plugin?

Regards,

Dave