One way is to create two different Styles: Forum and vBa. For your vBa pages use the vBa template. Because both styles inherit vB's width settings you'll need to edit a few vBa templates:
In the
spacer_open,
header and
footer templates.
Code:
<div class="page" style="width:$stylevar[outerdivwidth]; text-align:$stylevar[left]">
To something like:
Code:
<div class="page" style="width:100%; text-align:$stylevar[left]">
Change the "100%" to whatever dimension you want.