Not really.
Going to the Studio app - ToExtVXML[]. Coming back - caller_input and FromExtVXML[].
But I think you can do it mid application flow with ReqICMLabel - but I have never tried it and have never needed it. There have been some posts on the CVP Developer's Forum about this however, and you may want to read those threads.
But what is the issue here?
You pass down data as name=value pairs in the ToExtVXML[] and you get back data in any form of a structured string you like and can parse it. So you could pass down the value of the ECC var with a concatenate("varname=", ) and get it back in a "from" variable, parse it and set an ECC var.
Regards,
Geoff