Cross-domain policy for specific folder/URL

We're providing a service for app developers to be able to easily stream new content to their game, by providing an editor extension that bundles assets and uploads them to our service.

This is done by posting it to website.com/api via a binary element of WWWForm. Unity blocks this inside the editor saying "no cross-domain policy" (http://docs.unity3d.com/Documentation/Manual/SecuritySandbox.html)

We're able to get around that by adding the crossdomain policy file as suggested:

 <?xml version="1.0"?>
 <cross-domain-policy>
 <allow-access-from domain="*"/>
 </cross-domain-policy>

But that's a security risk since our login page is also on the same domain.

Adobe's standard actually lets you set policies by folders, as such:

domain.com/crossdomain.xml

 <?xml version="1.0"?>
 <cross-domain-policy>
 <site-control permitted-cross-domain-policies="all"/>
 </cross-domain-policy>

domain.com/api/crossdomain.xml

 <?xml version="1.0"?>
 <cross-domain-policy>
 <allow-access-from domain="*"/>
 </cross-domain-policy>

But Unity doesn't seem to even notice this. Here's the Editor.Log, after setting ENABLE_CROSSDOMAIN_LOGGING to 1

 Received policy
 Parsing: cross-domain-policy
 cross-domain-policy
 Parsing: site-control
 site-control
   permitted-cross-domain-policies: all
 done parsing policy
 crossdomain.xml was succesfully parsed
 About to parse url: http://localhost:8080/api/
 Rejected because there was no AllowedAcces entry in the crossdomain file allowing this request.
 Rejected because no crossdomain.xml policy file was found

Is there any way to set a policy for a specific folder/URL? It seems like our only option is to create a subdomain