Originally Posted by
Often1
(snip) ... These things are best dealt with before the cabin door closes and ... (snip)
Again, be firm. Ask if the Captain and GA can do anything. ... (snip) ... Remember, no threats. Simply polite statements. ... (snip).
Don't ask if. Instead tell. Don't give them a chance to answer no to a question (can do anything) whose real answer is yes.
If there are no empty seats then come out and suggest that they ask for volunteers to free up an empty seat for you.
There are oodles of other things they can do to fix the problem but in the name of the KISS principle don't rattle off the whole list.
Before the door closes the ground complaint resolution officer at your request should come through it to view the situation if an empty seat was not found for you prior to this.