Okay, how about this.
"Anyone who does not attend the tournament will be given 100 gold. Evilstani is about to attack and we want to make sure that those who have mobile units get the gold they need."
Just look at the character list and give gold to those not attending. That way, you are sure not to make anyone feel bad, and you get the same desired effect of funding the people able to move for defense. No need to make an announcement about it.
