Hey Daniel -
You've nailed it - URL actions which put your values on a querystring which get parsed by your webapp is the best (only!) way to go. There is no way to force this action to be a POST - you're stuck with GET
Are you passing some sort of GUID/PK value into your LOB app? While not spacious, 2K characters is normally enuf to pass values
There is no SDK for Tableau.
Yes we were looking at passing PK values into our LOB application. This will work if there are a small to intermediate number of values to pass in.
This won't work if we were to attempt to pass in a large number of selections. For example I was testing with a scatter plot, where each point was a customer. With 5,000 customers on the scatter plot it was quite easy to exceed the 2,000 character limit.
Thanks for your time and information.