Define 'impromptu'.
I know of one method that would visually accomplish this, but it does use a gimmick which would be easy to ring into the deck and cause the effect. I will also say it's not a good/developed method and I wouldn't want to employ it except in very limited circumstances.
Trying to place the cards on the ground probably removes this from the realm of properly 'impromptu' magic. Meaning that you're trying to take a regular deck of cards and make it cut itself from a distance with no outside gimmicks. I can't think of a way that would be possible.
I do know of an impromptu haunted deck, but it has to be in the hand of the performer.