Default Domain w/Domain Mapping

I'll looking to have domain mapping (like the other WPMU Plugin available for download) plugin allow for redirects or aliasing, so I can choose a default domain if using more than one tld without having to add a 301 redirect.

So if I add domain1.com, and domain2.com, I'd like to be able to set my default domain to domain1.com and have domain2.com forward to domain1.com (or even my original subdomain). My question is is this available via a configuration setting to allow multisite users to choose their default domain, or should I revert back to the non wpmu-domain mapping? How is this handled if I'm using the Pro Sites plugin?