jQuery Grid Plugin - jqGrid

Formatter automatically appends id=n, where n is the primary key of a row if the formatter is set to showlink.  This happens in other places as well (edit, search).  Would it be possible to set the name of the primary key when initializing the class?  If I'm displaying a list of customers and I want to see their invoices, and I set a column to showlink (say, the number of open invoices), I want to call a script in the format invoices.php?customer_id=n, not id=n (which may give me invoice number n, if anything).  This is further complicated if I'm showing a list of products sold, and I want to see all the invoices where they were sold.  If I set showlink, the default comes out to invoices.php?id=x

Obviously, I can add my own extra parameter to this id=n&id_name=customer_id.

Even better would be a template or sprintf that would define where I wanted the ID.  For example, I use a lot of rewrite rules, for our news table I don't want articles.php?id=777&id_name=article_id, I want the much cleaner

/news/article_777.html

Also, can you explain showaction?  I can't figure out how to use it.

Thanks!

Tac