If you allow the sludge to sit, until the solution turns clear yellow, you will see a bead of mercury at the bottom. RECOVER!
Have you tried adding aluminum strips to the sludge and allowing them to sit for 8 hours or so? The posts that lugh reference above indicate that all the Hg will ultimately amalgamate back to elemental Hg in the presense of aluminum strips. Now maybe the amount of aluminum used in the reaction is enough to convert ALL the HgCl2, I don't know. Anyway, it might help to recover more mercury (disclaimer: this is blatant speculation on my part).
Ok, second question...
The bucket amination calls for 800mg HgCl2. I realize that everything from the MM synth was scaled 2x, but is it really necessary to scale the HgCl2? It seems from what I've read that you'd do just as well to leave it at 400mg.
A watched pot will indeed boil.