For a human contolled group:
Assign the "Transport Unload" waypoint to the chopper, and assign the "Get Out" waypoint to the group inside the chopper. Normally, the Get Out waypoint only disembarks the leader, he has to order his group to disembark. However, if it is AI controlled, the whole group will disembark. However, there is a trick I found out:
Place a trigger on the invisible H that is triggered by your group leader when ihe is not inside the chopper anymore by setting the condition to: "vehicle (Ldr) != helo" ("Ldr" and "Helo" are the Group leader and the chopper), and have him execute the "eject script", which is also used to drop parachuters. Just search the scripts for something like "heloexit.sqs" or "eject.sqs".
Works for me just fine, but it will take 6 seconds for a whole group to unload... I need a 1 second spacing between the ejections, maybe a shorter time will work, but it did not work for me with just one AI in my group. The chopper took off after I disembarked and my second soldier fell down...
Another advantage is, that as a human controlled leader, you do not have to order your group to get out. They will do it by themselves because of the ejection script...
The chopper will fly straight to the LZ, but takes an awfull long time to descent...
I have included the misison as a pbo file. I used a 0.5 second spacing, and it takes approx. 6 seconds from touch down to lift off.