Central discovery service filter by role?

[Tom Poage]

I'm exercising the central discovery service (1.2.1) and attempting to
white list all SPs and a select handful of IdPs from a single/common
(remote) metadata source. Cf. wayfconfig.xml

"NOTE that the resulting metadata has to include any SP which may need
service from this DS."

Is there a way to white list by 'role' a la IdP EntityRoleWhiteList for SPs?

>     <metadata:MetadataFilter xsi:type="metadata:EntityRoleWhiteList">
>       <metadata:RetainedRole>samlmd:SPSSODescriptor</metadata:RetainedRole>
>     </metadata:MetadataFilter>

Not seeing anything I can recognize in the source, so guessing code
might be required.

Possible to build the union of two white list Filter's (alls SPs and
explicit IdPs)?

Doesn't look like the following works:

<MetadataProvider identifier=... url=... backingFile=...>
  <Filter identifier="white1" ...
  <Filter idenfifier="white2" ...

Or maybe there's a filter chaining entity in there (can't seem to find
guidance in the .xsd's).

Thanks for any guidance on this!
Tom.