Getting sitecategory name in scheduled script

I’m trying to implement a way of cross selling into our product pages.
IE: having a list of other categories the item is in listed on the product page with links to these categories.

At first I wrote a script which was ran each time an item was opened and then saved:

for ( var i = 1; i <= nlapiGetLineItemCount('sitecategory'); i++ )
{
  text = nlapiGetLineItemText('sitecategory', 'category', i);
  strCategories += text.replace("'", "\\'");
  if( i != nlapiGetLineItemCount('sitecategory') )
   strCategories += ' | ';
}

this got me a list of categories the item is in like 'Cat : Sub Cat 1 | cat2 : sub cat2'

This was becoming unmanagable and so i decided to make it a scheduled script, the problem is the same code returns for example '1075 | 57734'.