*Currently,* (as of 14w08a) this does not appear to be possible. The changelog for 14w07a specifically says that NBT matching works for `/testfor` and `/testforblock`. It doesn't appear to work in any other command.

[From the changelog:](https://mojang.com/2014/02/minecraft-snapshot-14w07a/)
> * The commands /testfor, /testforblock and /clear can now test for partial matches of NBT lists

It specifically says those commands, and doesn't mention the `@p`, `@e` or `@a` selectors.

This is very much a *currently,* as are all snapshot issues. As it is, it doesn't appear to be possible right at this moment.