This is not currently possible, but might be reconsidered in the future.
It used to be a feature, but there was too many problems with trying to allow this because of game issues and how the skills people wanted to use didn't actually work well. Basically, a skill like Ice Nova is perfect for it, but not everyone uses that. There have been map issues where using a projectile on a breakable resulted in the terrain eating it and other oddities like that. The actual chest targeting in the game itself is imperfect (has several known issues with highlighting the correct breakable) so there are other workarounds in place to help avoid those issues (at the expense of people complaining about them.)
