Completely optional sidebar - how do I do it?

[Loony BoB]

For quick reply on our forums we use this plugin...

global $vbulletin;

if($vbulletin->userinfo['userid'])
{
if($vbulletin->userinfo['field10'] == 'Yes')
{
$vbulletin->options['quickreply'] = 1;
}
else
{
$vbulletin->options['quickreply'] = 0;
}
}
else
{
$vbulletin->options['quickreply'] = 0;
}
on showthread_start. This code disables quick reply entirely as a user editable option (along with a profile field, obviously in our case this is field10).

Is there a similar way to disable the sidebar entirely as a user option? Right now we get a lot of complaints about the sidebar by some members while others really enjoy it. The main reason for the dislike seems to be that when you hide the sidebar, it still initially loads up and then hides after loading is complete, meaning it kind of "flashes" the user. :p What I want is to have the entire sidebar disabled as a user option, but enabled by default. That way if people continue to get annoyed by the serial flasher that is the sidebar, we can just instruct them to disable it by default by editing their general settings/preferences.

I tried setting it ups as...
global $vbulletin;

if($vbulletin->userinfo['userid'])
{
if($vbulletin->userinfo['field40'] == 'Yes')
{
$vbulletin->options['sidebar'] = 1;
}
else
{
$vbulletin->options['sidebar'] = 0;
}
}
else
{
$vbulletin->options['sidebar'] = 0;
}
on forumhome_start but it did not give me any luck. :( field40 is obviously the field we have set up similar to our field10 for quick reply.