Honestly, I don't think that you can use the sample questions to tell you what your DS's scores would be on the actual EXPLORE. Perhaps someone can give you an idea of the conversion, but I don't think it would be particularly meaningful. It's just not a large enough sample of questions. In addition, part of the challenge for many kids is pacing and having the stamina to get through 2+ hours of the test.
Yes, it's a bit of a nuisance, but why not have your DS take the EXPLORE for real? I arranged testing through Belin-Blank and it was not that onerous. Not only will you satisfy your curiosity, but you'll have actual scores that might be of some help with school advocacy.
