I asked a similar question and Jayderyu answered with this, I hope it's of some help:
"On ANY multitouch event
compare two values(touch.index = 0)
On Touch Start
touch.index = 0
on Touch.End
touch.inde = 0
Is in Touch
touch.index = 0
Is Touching object
touch.index = 0
this shuold always evaluate to the touch object of 0.
This however has one draw back and I don't see away around it.
1. Touch to screen. This is index 0 which we will name A
2. Touch another finger to screen. This is index 1. with say name B
3. Untouch finger A. Finger B now becomes index 0
that as what I can figure the best alternative. There is no simple option to just disable Multi touch in the properties. If you want a true single touch experience and avoid the index shifting in above example. You will need then need to be a little more advance be associating a Touch.index with a Touch.ID. but then your getting into more work."