Question about SSML files and the prompt tag in VXML

Is there really no way to specify a URI for an external SSML file in VXML
2.0? I am looking for  an "src=" attribute of the <prompt> element that
could specify resources whose mime types are either "application/ssml+xml"
or "text/plain". This would be analogous to the "src=" attribute of the
<grammar> element that takes a URI specifying a resource whose mime type is
"application/srgs+xml" or "application/srgs". Currently it appears that all
Speech markup must be in line.

Am I missing something?

Thanks,
Mark Clark
Cisco Systems
Software Engineer, CCBU
(408) 902-3450