How I’d go about doing this is by placing the gradient on a lower layer than the letters, making all of their shapes, then selecting them with the magic wand, hide the upper layer, invert selection, and delete from the gradient layer. This way the gradient will be cut into the shape of the letters.
Sure, it’s not the most elegant way, but it works 
Also make sure to save a Work-in-progress file before the whole operation, incase you want to go back and change their silhouettes.