It depends how many times this is to be done. If it is to be many times then, as bedges says, you will have to "spawn" them.
To do it just once needs less scripting:
1. Place a trigger: Radio Alpha, Repeatedly and On Activation: [] exec "help_me.sqs"
2. Place the three extra soldiers somewhere far away in a separate group. Give them names: soldier1, soldier2 and soldier3.
3. Create the script as a text file:
help_me.sqs? (count units player) > 9 : exit
1 setRadioMsg "NULL"
[soldier1, soldier2, soldier3] join (GrpNull)
[soldier1, soldier2, soldier3] join player
soldier1 setPos getPos player
soldier2 setPos getPos player
soldier3 setPos getPos player
The script first checks if there are nine or fewer units in the players group, since 3 are to be added and the maximum in any group is 12.
It then hides the radio option, assuming that you used Radio Alpha. If you used something else, you will have to change the number in the
setRadioMsg line.
Finally the troops are teleported magically to the players location.