create/add a non existing key to mouse

create/add a non existing key to mouse

The question is a little weird, and i couldn't find an answer on google
My mouse have 10 buttons so i can modify them to simulate other key
presses for example, i could put the "Button 1" of my mouse to enter "A"
everytime i press it, then i would go into my game > options > key mapping
> jump and enter "A", so everytime i press the "Button 1" of my mouse it
would jump,
But i dont want to have a conflict between games/programs, so i want to
assign for example the "Button 1" of my mouse to the non existing
"Custom_key_1", so i go into my game > options > key mapping > Jump > i
press the "Button 1" of my mouse and it will appear: "Jump: Custom_key_1",
then in every other game if i press the "Button 1" nothing will happen
because this key doesnt exist, so i wouldnt have a conflict...
Is there any program wich create a 'virtual button', wich i could assign
to my configurable mouse buttons?