The 3-point stance is the closest substitute you have
One hand down, lead foot forward, back knee up, explode out at a cue. This drills the set position, the drive angle, and the first five strides about as closely as anything short of real blocks can, which is why most programs use it as their default when a track is not available. Coach it exactly the way you would coach a real block start, hips slightly above shoulders, weight forward, head neutral, so the pattern you groove is the right one.

