I play tug all the time. As soon as I see my boy getting flat or bored I'll pull out a tug toy to motivate him. You can do this at trials...just not inside the actual ring. I also try not to sit around at trials for too long. One time I did a Rally trial in the morning, and should've been in the obedience ring like 2 hours later (with the same judge) but he was SUPER SUPER slow and it ended up being about 5 hours later. We qualified for our CD leg...but with a super low score and 6 out of the 8 dogs NQ'd.
So if I'm at a trial, I'm constantly playing/training him every 15-30 minutes just to make sure he doesn't get tired and bored.