When I'm at work, I access various intranet pages as well as the wider Internet through ethernet. However, the company LAN blocks some ports (e.g. Google Calendar). I can get to those through WiFi. So, I gave the Airport priority, and then using route add, I set up selective routing: all intranet traffic goes through the ethernet and everything else via WiFi: sudo route add 10.0.0.0/8 <intranet gateway>.

However, there are a number of intranet sites that have their own DNS; i.e., hr.company.com only resolves on the intranet. The only way that I can get the DNS to work properly is to add the internal DNS server to the Airport DNS listing, however I fear that when I go elsewhere and forget, this will break things.

What's the right way to get the DNS to resolve using this setup?