As Armsty says, group the first trigger to the scud and you'll get new options in the Activation box. However, that will make the scud start the launch procedure immediately, which may look a little odd. I would do it like this.
Trigger
Activation: scud present
On activation: [] exec "scud.sqs"
And the script, this is just a sketch, you'll need to alter it to make it work and to suit the circumstances
; this script makes the scud launch
~10
scudname action ["SCUD Launch"]
~4 (experiment to find the right delay)
scudname action ["SCUD Start"]
exit
Of course you could use a gamelogic with WPs instead of a script.
Check the FAQ - it has some scud tips.