Well put on all of the various reasons why not to house them together, but we disagree on one point. You are very right that these large constrictors (and all other animals) can respond to conditioning. That is the very reason I always feed outside of the enclosure, but in a separate feeding enclosure. This feeding enclosure is the only place that the snakes are offered any type of food. With this method the cue for the snake to strike and eat is not the opening of its enclosure door, or seeing a hook or my hand entering its living quarters. The cue for feeding is the environment of the designated feeding container and the entry of a prey item. This method may increase the amount of time it takes for feeding, but has allowed (for me and the snakes I have worked with, at least) for regular handling and trouble free feeding. I should note that I do allow time (a few hours) after feeding for the food to settle before attempting to put the snake back in its enclosure.
I, in no way am trying to imply that this is the best method, it is only what has worked for me, and it is very possible that I have wasted many hours in feeding this way. We all develop our own husbandry methods over the years to suit our individual needs.
-Wusstig