Hi Andrew,
Indeed I think you already found what you were looking for: if you subscribe to the event raised by sam queue, you'll be able to catch the sales order identification number sent back from ERP. But this seems to be quite a lot of effort when you can simply use the Lean Order approach instead of transaction launcher. Of course there are some minor constraints, but the look and feel is definitely better, and you won't have to struggle to get the information you want: everything will be accessible through common bol entities...
So you might want to give it a try.
Cheers,
Nick.