Not possible, but you could just add the volume up/down commands to the start/end of your regular activities rather than having seperate activities for it.
If you only need to raise/lower volume in certain circumstances, how about 2 "Watch TV" activities..ie "Watch TV" and "Watch TV low vol" or something?
If you only need to raise/lower volume in certain circumstances, how about 2 "Watch TV" activities..ie "Watch TV" and "Watch TV low vol" or something?