You can't currently. Planning to implement that as an alternate route with one of the add-on packs (which will be free to those who have bought the game; I call them "packs," but in practice the game itself will just get upgraded with the new content as each one comes out.)
Ah, ok. Yeah those are all about speed, prioritizing the right enemy, and maybe just a bit of save scumming. Don't just blindly attack: pay attention to where your multi-attacks land, and if one guy's about to go down, sometimes it's worth it to prioritize rushing him with a regular attack rather than waiting for your multi to recharge.