Okay, First run I think this works.
All I did was write this in the header of custom inserts for one forum:
<?php
$config['LEFT_COLUMN_BOXES']= array("portal_box_2","portal_box_1","portal_box_4")
?>
The syntax is probably not very clean.
But it allows me to use any island I want in a forum while still maintaining the default portal islands.
At least on the untouched column.
And the user can still turn off the column if they wish.
The tough part will be keeping track of it.
Can anybody think of a "Danger Will Robinson" with doing it this way.