sure jeff can chime in but you zap it with the actuator before putting on the dustcap you won't have time to put it on an center it before it hardens. you should have enough glue that comes out the sides of the dustcap that you can spray the actuator on it without taking it off.
but to answer your question if thte glue has not harden at all you can get a piece of tape about 2-3in an loop it so that tacky side is up not in, when done it will look like a ring, put it on your dustcap an lift up almost like a tape handle lol. if ya want i can post a pic up of it an you can see what i mean.