I actually do have a way i figured out a while back. It basically uses lag to your advantage. However, it may take a while to get it to work for even one, so i don't know about a multitude of them...i guess it depends on how much you're lagging at the time.
Anyways, while the pack is open, find the item covering the target. For example, let's say that there's a giant Gilded Chest laying on top of a bag, preventing you from opening the bag. You start grabbing and pulling at the Gilded Chest, like you are trying to remove it from the backpack as if it was your own. While you are doing this grab and pull motion, hit Ctrl + Shift repeatedly to cause all item names in the area to repeatedly pop up. Eventually, it will lag so bad that, believe it or not, the Gilded Chest disappears entirely. You can then freely open the bag and have a look around. However, whenever you close the backpack and open it again, the Gilded Chest will be back. I guess setting a macro for All Names, and spamming that along with Ctrl + Shift, would cause even better lag.
The player would have to be afk or just sitting still for a long time. This worked best with a sneaky fellow who had a macro that would automatically do quests in Heartwood for her. She eventually caught onto the fact that i was watching her get rewards for turning in bows, and so she'd try to hide the container which her macro put the good rewards in. I then was trying to move the blockage, and quickly move my cursor back to the container to open it before the blockage was sent back into the bag. That's when i figured lag would give me more time to click the container, and eventually the blockage just vanished completely lol. I've tried it multiple times, it's not a fluke...it works.
