Hi,
No there isn't - there isn't a concept of a window in there.
We were developing a "windowing" type system on top of tk2d, which would handle pushes and pops nicely. We never completed it though since Unity 4.3 came out and introduced the sort order stuff. If you want to imply net something similar, I recommend using sort order for most of the UI, and then have a little window manager that pushes and pops stuff by fixed z increments. Every time you push something all the rest of the "Windows" are pushed back by a certain amount in z, and every time you pop it it comes back forward by the same amount. This simplifies stuff greatly.