1st:
Put together a unit in the Virtual Arsenal, having only a sidearm
2nd:
Create a unit in editor, paste the exported script into the unit's Init field, and create a waypoint with "safe" or "careless" behaviour, or put command into Init field for it.
3rd:
Run the mission and see the unit keeping his gun in hand
4th: (Solution)
Add commands to unit's Init field: this addweapon ""; this removeweapon primaryweapon this;
Now the unit should spawn unarmed, sidearm being in it's holster.