Setting up Preferred Search Center for My Sites defaulting to default public URL

I'm having a problem correctly linking the My Site preferred search center to our main portal application's search center.

In the User Profile service, Setup My Sites link, there is a place to specify the preferred search center. No matter what you put into this field, it will automatically change to whatever the public URL is of the default zone for the web application of the search center you are trying to link it to. However, for our purposes, we need to use the search center with the Internet zone public URL, not the default zone public URL.

Here is my current AAM setup for the main portal web application:

Here is the current AAM setup for the My Sites web application:

We reverse proxy everything through an ISA/TMG server, so the public access URL to the main portal ishttps://insideisatest.company.com and the public access URL to My Sites ishttps://mytest.company.com.

So right now, the preferred search center for My Sites is forced to be https://sptestapp01.adtest.company.com/searchcenter/pages, but we need it to behttps://insideisatest.company.com/searchcenter/pages.

Does anyone know how we can do this?  We can’t change the default public zone (https://sptestapp01.adtest.company.com), but cause that is needed for proper search results as well as keeping contextual search working.