There is actually a book that talks quite a bit about this subject and about a few clever ways to teach the commands when you're in the city and, obviously, have no stock:
http://www.amazon.com/Shorty-Guide-Raising-Young-Herding/dp/193194265X
Fair warning, there's a lot of dominance based training in the book. I was rather surprised by it though I don't know why as most older herding people believe you can't teach a dog without showing it who's boss and giving it a few come to Jesus moments. Don't take it as a literal how-to, just take the ideas she gives and apply them to your own life. What's really interesting is how she has an immune disorder and did a lot of training without really being able to even get out of bed, so I think there are really valuable ideas in here.
No, I absolutely don't think you should only teach these behaviours on stock. You certainly could, but if you don't have access to stock, I just can't come up with a very good reason to wait to teach the necessary behaviours. I honestly can't think of any sport that involves something that couldn't be broken down and taught as foundation behaviours to build upon at a later point... And laying a foundation just makes it easier. Think about it: would you rather walk into a pen with a dog who knows how to flank appropriately but might need arousal work to be able to perform them, OR walk in with a dog who needs arousal work and also needs to be taught the necessary behaviours from scratch? I'll take the former.
IME the foundation is a two-fold teaching your flanks, walk up, back, and that ilk - and also learning your dog, how your dog works, and how to work with your dog. You can't really teach balance without stock but you CAN begin to teach balance without WORKING the stock, something I started with P his first or second week with me.
As for conditioning, I think it would depend on the individual dog in question if there's anything specific that would need worked on versus just an overall fit dog with strength and stamina - you might reach out to Robert Porter and ask if he has any herding clients and what kind of exercises would be best to look at!
This is actually my favorite book on the subject but it's rather overwhelming because it's very spot on and detailed, but doesn't make a lot of sense if you've never worked stock or seen it done (repeatedly and by someone who knows what they are doing.)
http://www.amazon.com/Herding-Dogs-Progressive-Vergil-Holland/dp/0876056443
And I've heard great things about this book but I don't own it:
http://www.amazon.com/Stockdog-Savvy-Jeanne-Joy-Hartnagle-Taylor/dp/1577791061
