Well, you can do something that will kind of work. Since you won't know where the volume is at any given time, the first command sent after power on should set the volume to a level you're comfortable with. From there you make the vol up command be the next level up and the vol down command be the next level down. If either of these buttons is pressed you then do a page flip to another page that's exactly the same except it has the next level up for volume up (if volume up was pressed) and the previous level for volume down.

Another way would be to build a gigantic macro, with a flag for each possible volume level. Whatever flag is active, would dictate the results of a volume up/down push, then you would set a new flag for the level you're sending. I don't like this method because the macro will get so big as to be almost impossible to decipher when you're building it.