Odd, both me and my friend were trying mousewheel when the other was bleeding and all we could do was go through each others packs, no matter where we were standing... I'll have to try again tonight.
Since the 1.5.8.2 patch I've been struggling to use items such as bandages or blood packs on other players. I'm not sure how that is supposed to work with the new right click items to use. Can anyone explain how to go about it now?