Magento – Hide Specific Attribute Filters for Each Category

I would suggest that the best way to achieve this would be to rewrite Mage_Catalog_Block_Layer_View in a custom module and then change the function getFilters so that it looks something like the following:

public function getFilters()
{
    $filters = array();
    $filterableAttributes = $this->_getFilterableAttributes();
    foreach ($filterableAttributes as $attribute) {
        $filters[] = $this->getChild($attribute->getAttributeCode() . '_filter');
    }

    if ($categoryFilter = $this->_getCategoryFilter()) {
        $filters[] = $categoryFilter;
    }

    return $filters;
}

edit the file /app/design/frontend/{package}/{theme}/template/catalog/layer/view.phtml and replace this line:

 <?php if($_filter->getItemsCount()): ?>  

with

 <?php if($_filter->getItemsCount() > 1): ?>

I only see one problem with this approach.
If all your filters have only one option they you will still get the section title

<p class="block-subtitle"><?php echo $this->__('Shopping Options') ?></p>

But this can easily be overcome if you loop through the available filters and see if you have at least one that has the items count bigger than 1.