Something I've found to be very easy in this case is using a trigger_changetarget. The trigger_multiple first targets nothing. When you pick up the suit you trigger this trigger_changetarget, wich changes the target of the trigger_multiple to whatever you want.
I believe it was done the same in Half-Life's intro. Without having the suit, a sentence was triggered so the barney said you needed the HEV. After picking up the suit a sequence was triggered so he would let you trough.