Hi,
Dealing with individual finger id is mandatory, else it's unreliable, this is the way unity works, and actually logical, since you can have many simultaneous touches, you need to keep track of the right touch for a particular button.
I don't think there is a simple way even in scripts. If you find script that does what you need, let me know, I'll see how it's been made and work out a solution in PlayMaker if it turns out simple.
Bye,
Jean