I need your help with the gwt requestfactory

**considering following scenario:**  

I get an existing entity (let's say a invoice) from the server:

```
InvoiceEntityProxy invoice = request1.getInvoice();

```

I want to make some changes, so I edit it with a new request:

```
InvoiceEntityProxy editableInvoice = request2.edit(invoice);
//make some changes to editableInvoice

```

Now I send the changes made with the second request to the server, to create a preview:

```
request2.createPreview(editableInvoice);

```

When the request is sent, the invoice proxy is frozen and I re-enable editing by assigning the proxy to a new request:

```
editableInvoice = request3.edit(editableInvoice);

```

If everything is okay, i want to update the proxy and send it to the server, using the latest request:

```
request3.update(editableInvoice);

```

But the changes never arrive on the server, because the latest request (request3) doesn't know anything about the changes made to the proxy assigned to the request2.  

I thought about following solutions:

1. I could redo the changes on the latest proxy. But for that, I've to iterate over all attributes and set them again (not very friendly solution, because I've to adjust the method each time I add some attributes to the proxy)
2. Another approach would be to send the proyx without an id to the server and send the id as second parameter of the update-method. But this would be a shame, because not only the deltas would be sent to the server (which is one of the greate features of the requestFactory).

So what is the best and most common practice to let the request3 know about the changes already made to the proxy, when it was assigned to another request.