auto_now = True on some updates, False on others?

[nwal...@sprynet.com]

I have a table where users can add their own rows, but the admin must
approve it.
So my model contains this:
dateAdminDecision = db.DateTimeProperty(auto_now=True)

Obviously, at first, every row, even when the users added their data,
was getting set to this date.
But I only want the date to be set when the Admin approves the row
using a special Admin form.

What about the approach I have tried below, so far it seems to be
working. Is this technically called inspection or reflection? I use
the same template, but two different forms classes, each form class
has different "exclude"s on it so the non-Admin sees a different set
of fields than the Admin-user.

if users.IsCurrentUserAdmin():
MyModelName.__dict__["dateAdminDecision"].__dict__["auto_now"] =
True;
form = AdminForm(data=request.POST or None, instance=conference)
else:
MyModelName.__dict__["dateAdminDecision"].__dict__["auto_now"] =
False;
form = UserForm(data=request.POST or None, instance=conference)

I saw in some other post that auto_now maybe going away soon. I'm
creating this app for GAE right now, but want to think broadly of how
I might do this on an LAMP type server as well.

Thanks,
Neal Walters