Just to note the power doesn't actually say you MUST pull the target, it says;
Hit: Constitution modifier damage, and you pull the target 1 square.
Or 4 squares if you augment by 1 or 2.
To answer the second part of your question. The RAW for forced movement states;
Distance in Squares: The power you’re using specifies how many squares you can move a target. You can choose to move the target fewer squares or not to move it at all. You can’t move the target vertically.
Even if the power says you pull the target X squares you can move them fewer if you choose.
