Magento - Update main product price to include selected related products?

Anyone have any idea how this would be achieved.

I want to have it so that when a related product is selected it updates the price of the开发者_开发技巧 main product, as when you click to add everything that related products price will contribute to the price.

Any help appreciated.

Chris

Magento's cart pricing rules could approximately accomplish this, as could use of a coupon. Obviously, both have their drawbacks, but neither requires code.