Weight painting question

I’m sorry if this is the wrong place to post this, but I’ve searched many places and found no answer, and it seems like a basic question. I’m worried that I am missing something very obvious…

Is there a way to paint weights to vertices that are behind faces? For example, if I want to paint both sides of a box at once, is there a way to do it without rotating the 3d view to see the vertices behind the visible part of the box? Or, another example, if I want to paint a vertex on a human model’s back but I’m looking at it’s stomach(so the vertex is “behind” the stomach), is there a way to paint it without rotating the 3d view?

In case anyone wants to know why I’m asking, I want to use the blur tool to even out weights on both sides of a thin object, but it seems there is no way to do so efficiently since I have to rotate the 3d view over and over to even out the weight on both sides.

Use “X mirror” in the Tool Shelf > Options,
You can also use Edit Mode to select vertices and edit both sides simultaneously, assign weights to your vertex group in the object data panel.

I don’t think there’s any other methods