From the photo's it obvious that there's decent access for you to put the bolt in from the threaded side so you can use it to jack the post open a bit (put a penny in the slot for the bolt to push against) and maybe buy yourself the needed room to slip the clamp across. Have you tried that yet?
OTOH, the entire seatpost seems hopelessly beat up, so maybe you need to ask yourself if you ever plan on using it again. If it's headed for the scrap bin anyway, why not spare yourself the grief and remove the saddle with a hacksaw?
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