If you are not perl averse, graph-easy (and the associated Graph::Easy package) can do exactly that:
http://search.cpan.org/~tels/Graph-Easy/
http://search.cpan.org/~tels/Graph-Easy/bin/graph-easy
On Mac you can install this with Homebrew and cpan:
brew install cpanminus
cpan Graph::Easy
It’s easy to invoke after installation:
cat dotfile.dot | /opt/local/libexec/perl5.12/sitebin/graph-easy