Sara B. - in other referenced posts, you said implementing contingency bids would probably be hard to implement. I don't think it should be too difficult.
1. Add an option to bids to, 'enter contingency bids'. Set them up in a sub-group linked to the primary item, or primary bid group.
2. Upon completion of the primary item, flow through the contingency bids - either cancelling or activating them dependent on the status of the primary item (won, lost). You already do something similar with bid groups.
Please take this as another vote for this option. I have a current situation where I have a bid group set up for a doll one of my friends has been wanting. Clothing accessories are also available for this item - and I don't need the clothes if I don't have the doll. This feature would be very welcome. Luckily, the doll is frequently available on ebay, so I'm fairly confident that if I win the accessory item and not the doll, the doll will eventually be won from another auction.