Buy something from category x and category y, save z percent

Hi there!
Now that I've got my site launched and live, I can tweak some of the settings. One of the things I've been meaning to do is to implement a discount when someone buys something from one of a number of categories, and something else from one of a number of other categories, saving a pre-determined percentage on the total amount of these two products. Make sense? Thought not...

Here's what I mean. Take category one as an example:

http://www.savshop.com/index.php?main_page=index&cPath=1_11_111

Now, if anything in this category or its subcategories is purchased along with, say, something from this category:

http://www.savshop.com/index.php?main_page=index&cPath=1_11_113

then the total amount of these products is discounted by a factor determined by me. Is this something Salemaker can do? I had a look but couldn't see it :(

Any ideas and advice gratefully received. Thanks!

Oh, think I've found it:

http://www.zen-cart.com/index.php?main_page=product_contrib_info&cPath=40_60&products_id=309

I'll try and report back :)

Although the mod didn't do exactly what I wanted, I thought about this overnight and bodged the same effect using attributes. Rather than processing an overall discount on the purchases, I ended up factoring the price of the second product down by the equivalent amount and adding the second product as an attribute on the first product. So, I achieved the same effect, but it requires a bit more admin from me.

On a related note, I had the pleasure of contacting 'swguy' about his mods and found him to be prompt, courteous, honest and trustworthy. Although no money/code changed hands in this case, I get the impression he's a thoroughly decent guy to deal with. Thanks, swguy!