yes, that can be done quite easily. You need to be setup for C++ programming, please see:
http://jevois.org/tutorials/ProgrammerVbox.html
http://jevois.org/tutorials/ProgrammerSetup.html
Then you need to add a member function
void process(jevois::RawImage const & input) override
{
...
}
to the DemoSaliency class in DemoSaliency.C
This function will be called by the JeVois core software when running in headless mode. To write the function, you take the other process() function and copy that code, then delete everything that involves the output image (outframe, outimg, etc).
Looking at the code at
http://jevois.org/basedoc/jvpkg_2modules_2JeVois_2DemoSaliency_2DemoSaliency_8C_source.html
it also looks like you would not need to run the saliency computation in a thread (which is parallelized with waiting for the out frame and drawing in it), you can just run
itsSaliency->process(inimg, true);
directly in the main thread of your process() function. I believe you then also should remove the call to
itsSaliency->waitUntilDoneWithInput();
as this is intended for use when itsSaliency->process() is running in a thread.
Have a look at this tutorial for a general idea of the various steps:
http://jevois.org/tutorials/ProgrammerSurprise.html