For those of you that want to bring real world difficulty into this, it's not nearly as hard to hit as you might think. I have a friend who is a private pilot. They have competitions for aerial mail drops at a local flying club where he used to live. They would fly a cesna (about 80 mph) over a field and they are supposed to drop a softball sized bean bag (with a colored ribbon streamer attached to ease spotting where it went) onto a target on the ground. The pilots dropped them by hand out the window WHILE flying the plane. Apparently, it would be relatively easy for a pilot to drop a molatov cockail onto a tank sized target (we were playing a WW3 game at the time when I talked to him about it). The altitude when dropped would be about 150' AGL. About 95% of the targets would land in a 20' radius circle of the target center.
Things going against the pilot are poor visibility due to wings and fusalage, you have to concentrate on flying the plane also, not perfectly consistent approach speed and altitude, variable winds. However, according to him, the streamer ribbon helped a lot to stabilize the trajectory.
A couple other things to keep in mind: terminal velocity for a human falling is 100-120 mph. A paratrooper jumping at 1000' whose parachute doesn't open has approximately 9 seconds from the monent he jumps until he hits the ground. Something like a brick would have a MUCH higher terminal velocity than a person. A penny dropped off the Sears tower will apparently go straight through the concrete sidewalk when it hits. I read on the news a couple years ago a frozen ball of sewage from a passing jet with a leaky lavatory hit a house and imbedded itself into the concrete floor of some ladies house after passing through the roof, ceiling, and living room coffee table (they though it was a translucent green meteor for about an hour, until it started to melt and it became obvious what it really was).
The applicability of all this to D&D is rather suspect though. Just let him drop 1, adjust for windage, and drop another ... geeze ... it would be simple.