Is anybody aware of a (sort of) standard way to deal with webservices that return ADO.Net datasets?

A "standard way"? I'd way what you have is standard, but more importantly, what you have works. As for being ugly, yes, your perl style style (if you can call it style) is ugly, but no uglier than SOAP.

It would appear that the perl community has forgotten about ADO.Net datasets altogether...

Why would you say that? You have a perfectly good way of dealing with them...