Ok how about aq css + if statement solution.
In your CSS file create a new style called center-main2.
The style for this will be a copy of center-main, except the margin will be 0 0 0 0px; instead.
Meaning the original one will be 0 0 0 250px;
Your if statement will be:
{if $main eq "product"}
<div id="center-main2">
{else}
<div id="center-main">
{/if}
Then the rest of the code...
Lets see if that works.