Famous last words.

It does look easy, but so did the first one.
Obviously you can do it however you like. For this we just ask that you do it this way first so you're shooting cold.
Shooting these challenges cold gives us really good feedback on what we need to work on. For example, the kneeling position should have the best groups because it's supported. Alas, so far that has not been the case.
Of course you can do whatever you like, but that wouldn't fit the spirit of the challenge, would it?
Does your indoor range have lanes? If it does, a lane divider could be used as a barricade. If there are no dividers, or they won't allow it, use a simple 2x4. Just stand it up, don't allow your shooting side foot to go beyond the 2x4 and shooter around it to the right (or left for lefties).
Yes, kneeling will present some challenges. Some just can't get down to the ground or if they do they can't get back up (even with the old man recovery technique

). So, yes, shooting from a chair is acceptable. Just don't use the table for support.