You can certainly hand knead the dough but it will take you ages to develop the gluten you need in brioche to get it smooth. Not to mention the enriched dough starts off as very sticky and it'll create a huge mess. It'll be your upper body workout for the week! You can also use a hand mixer with a dough hook, but be sure to look out for the physical signs of when the kneading process is done rather than basing it off of time. This also strains the motor of a hand mixer. I wasn't sure mine could handle it any longer.