I really doubt there's a way you can even force the server to acknowledge your position on demand because that would defeat the purpose of server only pooling the client every 0.3s instead of more frequently. There might be certain events that will get a response immediately (e.g. damage done to the a mob seems to always warrant immediate reaction) but I don't see how there's anything off GCD you can possibly use that will force a server update. Most likely the 'cast something when you're out' works because if you've time to cast something you didn't just barely beat the AE, so this in essence forces you to have less time than the castbar indicates, and it works out since we know you indeed have less time than castbar indicates so whatever trick that reminds you of that is going to improve your chances of dodging.