IIS dynamic compression for multipart/related

I'm using WCF and STS for security. I enabled IIS compression for the dynamic type thus

        <dynamicTypes>
            <add mimeType="text/*" enabled="true" />
            <add mimeType="message/*" enabled="true" />
            <add mimeType="application/x-javascript" enabled="true" />
    <add mimeType="application/xml" enabled="true" />
            <add mimeType="application/soap+xml" enabled="true" />
            <add mimeType="application/xop+xml" enabled="true" />
    <add mimeType="application/soap+msbin1" enabled="true" />
            <add mimeType="*/*" enabled="false" />
        </dynamicTypes>

and it works fine for metadata and STS service calls.

However for all the "regular" calls to the service I get a reply of type multipart/related containing the response and the security token together.

I'd like to get that response compressed if possible and I don't know how to do it. Setting the compression for everything

            <add mimeType="*/*" enabled="true" />

does compress the response but setting it to

            <add mimeType="multipart/related" enabled="true" />

doesn't.

The Content-Type of the response is

            Content-Type: multipart/related; type="applic开发者_如何学运维ation/xop+xml";start="<http://tempuri.org/0>";boundary="uuid:cb4a14b1-e162-41ee-80b8-752744d327eb+id=136";start-info="application/soap+xml"

Cheers.