Bug:

#+latex_header:\input{commands.tex} is not considered in
org-preview-latex-fragment. Reason: the fragment is generated in /tmp
from where the file commands.tex can not be found. In my case,
commands.tex contains essential latex-code for displaying the
latex-fragment, so I consider this to be a bug.

I have set the environment variable TEXINPUTS in
(org-create-formula-image) to work around this bug (see patch). 

However, this is the first time that I have written something like a
patch and furthermore I'm not at all familiar with lisp-programming. So
could you please have a look at my solution and tell me if it's complete
crap and how it could be done better?!

If it's no crap, I presume it should be submitted.

Thank you, Benjamin