How do I make meringue using a whipped cream charger?
Actually, this can be done but it may not be convenient to do if you aren't in a restaurant setting where this can streamline your process. If you take equal parts egg whites and sugar, beat them together, cook at 74C for 30minutes and then transfer them to the siphon and charge with 4 cartridges, dispense to desired shape, and then bake at 150C until set (this will vary depending on size and shape) you should be good to go. 

As I said, this is about the same as doing it the old fashioned way, time wise.