Is there an ExtJS DataWriter that can write all changes to all stores at once?

Question

I have a master detail form (think Invoice and InvoiceDetail). I have two data stores to go along with them both. The Ext JsonWriter object that comes standard with ExtJS is great if I want to send my insert, update, and delete statements back to the server in 6 separate calls (3 for each store). But what if I want to send all six at once?

The huge advantage to doing this is that I can use transactions on the database to roll back any errors in saving. This way I don't risk making only partial changes to my "Invoice."

I'm leaning towards creating my own custom JsonWriter, but I'm not sure.