Hi, Ian.
>Is there a way to establish a trust relationship with this SP without it supplying metadata?
No, isn't possible. But you can craft metadata manually, using any other SP's metadata as a template.
For example, here is simplistic metadata for Google Apps:
```
<EntityDescriptor entityID="google.com/a/domain.com" xmlns="urn:oasis:names:tc:SAML:2.0:metadata">
<SPSSODescriptor protocolSupportEnumeration="urn:oasis:names:tc:SAML:2.0:protocol">
<NameIDFormat>urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified</NameIDFormat>
<AssertionConsumerService index="1" Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST"
Location="https://www.google.com/a/domain.com/acs" >
</AssertionConsumerService>
</SPSSODescriptor>
</EntityDescriptor>
```
You could try to edit it into something reflecting your setup.
The question itself isn't really related to Gluu Server, and thus doesn't fall within scope of Community support. You could try Shibboleth-related resources in case of further difficulties.