Reply to Traktor Pro - Shorten loop towards the end

Hey guys!

I have a question, in VitualDJ I was able to map a key so when I pressed it, the loop will shorten to half but towards the end. For example: when I hit the key the loop goes from:

1 - 2 - 3 - 4
to
3 - 4
instead of
1 - 2

How can I do that in Traktor Pro?
Thanks