I would say first that make sure you are not trotting while heading home, but only away from the barn.
Then, I would ask him to trot, but only IF he is warmed up, relaxed and calm at the walk. If his head is high, eyes wide and ears swiveling all around while quick stepping down the trail, he's feeling good and ready to go and will not give you a calm trot. You may have to walk quite a while to get the edge off of him. But if you don't have a calm, relaxed walk you sure will not have a gentle trot. One buildes on the other.
If he relaxes and settles down, then use as little cue as possible to ask for the trot. If he moves through the trot into a lope, immediately turn him right there in the trail and circle him about 3 times in his tracks. Have him come to a complete stop after that last circle and be facing down the trail you were originally going. Pause for a moment and pat his neck. It is calm, happy school, not the princilpe's office. Then start walking. If he is calm, ask for the trot. If he moves out of the trot into a lope, repeat the process. In a short time he will figure out that changing pace without your cue just results in extra foot work and causes him to have to actually slow down and stop, which is the opposite of what he is after. It wont be worth all the fuss to him, and he will give up.
Some horses take longer than others, more circles, but it is an easy cause-and-effect way to get them to willingly change their own behaviour instead of mechanically changing it with bigger bits and tie-downs. Always train the mind, the body will follow. :)