No there isn't an alternate way to get in. The trick is to not get into the line until it starts moving.
People start lining up about 1/2 hour before they open the chain to let people into the amphitheater area. if you get into the line then, when the line starts moving, everyone wants to be first in and you end up with what you experienced.
We have been there mostly during Spring break and Easter (when it's really busy). If you wait until the first "wave" of people go in, the crowds are much less and it's not bad at all. In March, we went in with more of a trickle of people than a rush.
For leaving after the show, we wait until most of the crowd is out. That way, the crowd will get ahead of you and the people who are waiting are usually the more "mellow" group.
Another way to avoid a wait and crowds is to use one of the Fantasmic Dinner Deals. You eat at a specific Studio restaurant for supper and get seating in a reserved area of the theater. That allows you to arrive 1/2 hour early at an entry reserved for the dinner program people. We have not done the dinner deal, but quite a few people have, so you should be able to get a lot of input about it.