IdPv3: backing file mechanism for remote resources defined in services.xml?

[Kaspar Brand]

Specifying an http(s) remote URL via a <value> element in the
services.xml file (e.g. for shibboleth.AttributeFilterResources) is
working just fine.

What I'm wondering, however, is if there is a way to have a backing file
for such a resource? I'm mainly thinking of the case when the IdP is
restarted, but the remote resource is temporarily
unavailable/unreachable (with the IdP 2.x, there's
FileBackedHttpResource which helps in this case).

Kaspar