yes, there are a couple of mods that do this, but i would like this in vanilla game. I would like a new section of your party menu where you have your troop overview and you prisoner overview where you can drop cavalry units. (or a way to mark these units an other way)When chasing a smaler party there should be the option to send forth the cavalry to catch up.
2 ways to use them.
key+Lmouseclick: These units will chase the enemy party an harass them, reducing the party speed. (both sides take casualties over time)
Key+Rmouseclick These units will chase the enemy party and engage in battle. (best use for small groups)