[ic] Combine two fields into an SKU ?

[DB]

I'm looking for a way to combine a "brand" and an "item_number" (both
are fields of the products table) into an sku, so that a link such as:

http://www.website.com/order?brand=BrandA&item_number=1234&mv_order_quantity=2

Would add 2 of sku BrandA-1234 into a cart. It's possible that the same
item_number could be used by multiple brands, so the sku BrandB-1234
might also exist.

As with my last question, URL rewriting might work but I'm seeking a
more elegant solution. Any ideas are welcome.

DB