1. Open the editor, doesn't matter which island
2. Place down a Rifleman (doesn't matter which faction), set as Player and click Preview
3. Switch to your handgun
4. Injure yourself (use a grenade for convenience)
5. Use a First Aid Kit to heal yourself
6. At this point, the only way I've found to break out of the animation is by using the Action Menu to switch weapons. Throwing a grenade and reloading actually complete their respective actions but afterwards the unit returns to its frozen state. To my knowledge there is no other way to get out of this state unless you have another weapon already equipped in one of your weapon slots.