there is a addon for a G15 keyboard on curse-gaming.com just type in G15 in the search bar and you will find it. It puts a visual keyboard on your screen for the G15 buttons, and you can throw macros, skills and such into it. (it's like a extra action bar pretty much)
It's a must have for people with this keyboard im my opinion.

And this will accomplish what you are wanting, you can put different skills in the addon for each character and just press the button and it will do what you want it to do. You will need to bind ALT+CTRL+1 in your G15 profiler and in the wow keybindings, you will have the option at the bottom once you download the addon.

Hope that helps.