The situation you have is not so bad as you think. Some people rate 3200 at 800 to 1200 and get excellent results. Given that you rated it at 100 ISO you have overexposed by 3+ stops which is not really a big problem. I'd suggest you use Rodinal with a higher dilution, say 1 to 75 and dev for something like 10 minutes using semi stand development which should help hold the highlights. You have given no information about the contrast of the subject matter nor how you metered and these two factors will influence development and dilution.
I'm sure you will receive more suggestions and good luck when you finally dev the film. Please let us know how this turns out.