Level: HardStart as a French man (Duchy or King) in 1066. During the downtime before the Joust event, select "Your Knights" at the bottom right, and allow only your lowborn knights to participate, while disallowing everyone else.
Also, start your Tournaments in your capital. That way you can immediately invite a lowborn participant to your court and make him a knight, because your own knights will often not make it in the tournament.
Credit to
Bayek von Kuwaq on Steam for his
guide.