What kind of spool are you using, akimbo? The Delrin ones are very close to neutral -- they don't fall very fast. I have dropped them, and either I or one of my teammates has been able to recover them before they unspooled very much.
I'm still trying to wrap my mind around the set of circumstances that would require a very occasional and unskilled diver to deploy a bag underwater, and from a shallow enough depth to use the described technique. To me, shooting a bag is something you do to mark your position to a boat, or to make a no-reference ascent easier. I don't think a diver who can't learn to shoot a bag belongs in a situation where he's trying to do a direct ascent without reference -- and if he's in that situation, he doesn't need the additional task-loading of managing a bag. If the diver has been blown off a wreck, for example, it's not likely he's shallow enough to use this approach, and if he's terribly worried about the boat losing him, he's probably better off omitting the safety stop and immediately inflating a bag on the surface.
I really don't want to sound any more dismissive than I am, but in my world, we have a saying, "an equipment solution to a technique problem," with the implication that, rather than change your gear, you should improve your skills. People who can't shoot a bag really should avoid situations where doing so is a safety requirement -- stay with the guide with the float, or the guide who is going to shoot the bag, or stay on the anchor line on ascent.