Can't access variables in the advertisment HTML

[Retal]

I want to generate a random number and use it in the ad HTML to rotate banners, but I can't find the right hook to do it.

In a plugin (which one?!)

PHP Code:

$rotate_banner = rand(0,1); 


In the Ad HTML:

<vb:if condition="$rotate_banner">banner.gif</vb:else>...</vb:if>

Tried to use declare the variable as global, add it to $show, $vbulletin, but to no avail.

Anoyne has any idea?