How can I frequently practice openings that are more than 1 or 2 moves long? For a while, anytime I got the chance to play the Scotch, I would as long as my opponent (being black) played the moves.  If they did not follow the move order, I would just continue with something else, but I noticed, the more I play an opening, the better I get at it (This is obvious).  

Another way to view this question is, besides 1 or 2 move openings such as the English, Caro-Kann, Sicilian, Pirc, etc which obviously have been defined as being reached after 1 or 2 moves, how can I force my opponent and this may not be possible, it may just be by chance, to play moves up to the point where my opening is defined?  

Certain openings I have found this actually works pretty well such as the Ruy Lopez because it has such a natural move order 1. e4 e5 2. Nf3 Nc6 3. Bb5., but in other openings, it is not so easy.
This is where you have to understand the opening, not just play memorized lines.  If your opponent strays too far from the most popular lines, he's probably made an error.  It's up to you to understand the opening enough to punish him for it.

So you can't force him to play the line but you can make him wish he did.