I already have Episode 8 Winner Choi Junseop's encore stage here. Episode 11 Winner Maytree sang an English acapella so I didn't sub it. I'm not sure if I missed anything but this should be everything.
DO NOT REUPLOAD!
Subtitles by ohmygeona
Episode 1: Winner Kwon Hyukjun's encore stage
Episode 1: Skilled vocalist Kim Junhee's unreleased stage
Episode 4: Winner Lee Gyul's encore stage with Kim Yoon Ah
Episode 7: Winner Lee Inwoo's encore stage
Episode 10: Winner Goo Junghyun's encore stage