The problem with this plan is that I was never able to get Photoshop to import the EPS directly. I always got this error message:
Finally, today, I went looking for the solution. I used strings to see what the EPS Parser plug-in looks for. I found it in under a minute.
So, at minimum, this is what your EPS file must contain:
%!PS-Adobe-3.0 EPSF-3.0 %%BoundingBox: 0 0 width height %%EndComments
%%EndComments line is the one that I was missing. Make sure yours isn't missing it too.
In case you want to know more, these special comments (
% is the comment character in PostScript) are defined by the Document Structuring Conventions. EPS is an application of DSC.