On Sun, 20 Apr 2008 10:58:19 -0500, dpb wrote:

One can also simply use quikrete ready-mix to pack the whole and let it
set up w/ ground water as a simple expedient compared to mixing it.
Somewhat easier to retain the position and achieve plumb that way as
don't need bracing while the mix cures.

I recently used that to set a mailbox post.
Worked great! Get the post where you want it, pour in the dry mix and
pour water on it.