gpart usage during install

[Robert Simmons]

I'm just installing a 9.0-RELEASE instance in Virtual Box to check
things out.  I ran into something odd.  With 8.x I install certain
things into a geli encrypted partition.  To do this I have to use a
fixit shell and a manual install.  Now, I'm trying to do the same
thing in 9.0, but when I get to the partitioning stage of the install,
and I select the option to setup the partitions in a shell, I get the
following error from gpart.  What has changed?  What am I doing wrong?

# gpart create -s GPT ad0
gpart: arg0 'ad0': Invalid argument