As far as I know, blocking backdoors with siege engines during siege is against the rules for it prevents people from clicking the door and - well - *using* the said door.
If that is true, shouldn't it be also against the rules to put a fat orc at the door and have him jump nonstop, so that people couldn't use the door just the same?
If that is also correct, I have a suggestion that might rid us of this behavior and exclude the involvement of game masters who are so few that you can never get in touch with one when someone exploits.
The suggestion is this:
Add to backdoors the code that bumps people away from the expedition quartermaster.
It will provide just enough room for the cursor to make the door clickable.