Resize braces arbitrarily

I'm trying to get arbitrarily big braces in some graphs I have to make, using Inkscape with the PDF+LaTeX option. The problem I have is that simply resizing a bracket makes it stretch:

I'm aware that this may sound like an Inkscape question, but I'm trying to solve it with LaTeX (as opposed to a vector graphic approach).

So, is there a way to arbitrarily "resize" the brackets without deforming themspelling? I'm thinking about the end result of the align environment (vertical) or overbrace/underbrace (horizontal), but without really using any content to expand it (hence, arbitrarily). Something like:

-

\documentclass{article}
\begin{document}
$\left\{ \rule{0pt}{4cm} \right. %Change size as necessary$
\end{document}


You can use something similar for the horizontal version.

\documentclass{article}
\begin{document}
$\underbrace{\rule{8cm}{0pt}}$
\end{document}


Note that the height of the vertical version is double the height of the rule, whereas for the horizontal version the rule and the brace have the same length.

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To get an invisible vertical rule -- a "strut" in typographic jargon -- that's 8 cm tall in all and extends 4 cm below and above the baseline, on would need to type \rule[-4cm]{0pt}{8cm}. – Mico Aug 14 '14 at 16:33