I have been playing with something similar. My goal is to get the Product cost into my transactions table so, rather than try and expand it out, I am going to join it into the Transactions table with the Interval match, then I can drop the Product Cost table:
From temp_ProductPrice.qvd (qvd);
Outer Join (Orders)
Left Join (Orders)
Drop Table ProductPrice;
Drop Fields StartDate, EndDate;
See how that works for you.