Keyboard Maestro can press and hold a letter.
The key will only be held down until:
- The macro finishes
- You type the same key (manually or via Keyboard Maestro)
- You release it with another Type a Keystroke T action.
And Keyboard Maestro can drag the mouse.
Whether any of this works with Photoshop is anyone's guess. It is highly dependent on exactly how Photoshop behaves and that is far from predictable. Other than trying it and seeing, there is no way to know if it will work.