I have one that I use on my gelding for XC competition only. At home he schools in a snaffle. When I do use the elevator, I have one rein on the large snaffle ring and another on the ring right below it. I rely primarily on the snaffle, using the curb rein only when I absolutely need to. This might be something you want to try so you can ride him with the snaffle action most of the time, only implementing the leverage when he gets strong and needs a check.
If he were mine, I would put him in a snaffle, but obviously that's not an option if your trainer won't allow it.