Well, the short answer is, i don't know, - not without a lot of digging about.
Someone from Webassist may be able to offer more insight.
Honestly, I dont really like the master/detail that dw sets up, and if you have dataassist, you would probably better create the master page as you have outlined, and create the detail page separately, simply by filtering the recordset with appropriate url parameter, its not too difficult.