The only adjustment to a Toss 1 arm Stretch from a Toss Stretch is the grip. The toss itself should be exactly the same. 
Flier - Fliers, just as you did for the Toss Extension, wait for the flick at the very top of the toss. Remember: DO NOT pull your liberty early. Once you have flicked, go ahead and pull your stretch position by lifting your left leg up so that it is straight to your hand. Do not drop your chest.

Base - Approach a Toss Liberty just like you would any other toss stunt. Keep in mind that one should not cut the toss short. Follow all the way through to the top.  Once the Flier has pulled the Liberty position, spot their foot. It is important that you spot the foot in order to find the correct grip position. Your arms should be completely extended at this time. Drive your hand through the middle and keep it above your nose.  Grab the foot with only your right arm and aim for the middle back of the foot.  Squeeze and shrug up hard through this stunt due to the fact that you only have one hand on it.   
NOTE- It is important that you drive the toss completely to the top.

NOTE- Fliers, if you pull your Liberty position too soon, it will cause you to have a shortened flick.

NOTE-Spotting the foot is also a very important key. Bases slow the stunt down in your mind and watch your hands all the way to the foot. This will ensure that you have proper grip.