You can set the velocity in a direction with
a = angle(sprite.x, sprite.y, mouse.x, mouse.y)
Set velocity to 100*cos(a), 100*sin(a)
Impulse is more like adding to the velocity so that could be done with:
Set velocity to sprite.platform.velocityX+100*cos(a), sprite.platform.velocityY+100*sin(a)
Or something like that. I may have the names wrong.
For either 100 is the strength of the impulse.