One thing which comes to my mind would be DoubleCommand, but iīm not sure if it can do what you want.
Could also be useful
For G700(and most other keyboards) there is Logitech Control Center for OSX from Logitech.
Look for LCCKCHR.rsrc. Drop this file into /Library/Keyboard Layouts, logout and login and you have a few more options in the International System Preferences under Inputs.
Thatīs the only things i can think of, if that doesnīt help i hope someone else has a solution for you ;)