Lock part of an object so that it doesn't scale I'm trying to draw an object that has a lot of tubes of different heights. Those tubes are all exactly the same, with a hole on one side at the bottom. 
The holes of all the tubes should be exactly the same, and only the height of the tube change from one to another. 

Tube looks about like that:


Now, the question, since all the tubes are the same, I'd like to have them linked, so that if, in the future, I'm modifying something on one, it affects the others. But, if I do Alt+D and try to scale the tube, the hole at the bottom gets elongated, which is something I don't want.

So, is there a way to "fix" the size of the hole, and having the scale change the height of the tube, without deforming the hole.

EDIT: To make it a bit clearer, a very important point is that I want a linked-copy of the tubes. I want that if I change something in the tube, for example the shape of the hole, this change affects all the tubes. The only difference that the tubes will have will be their height (above the hole).
I created the dynamic length pipe with two objects. The first object is one unit long, only large enough to house the hole at the end. The second object it just the tube, easy to change the length, via scaling or inputting dimensions.

The way I link the two pieces, is with a Child of Constraint (scroll down to the bottom of answer).
Normal parenting would influence the scale, but with a child of constraint (CoC) each of the transform operations and channels are selectable.
Add a CoC to the hole object with the Target set to the main pipe.  Uncheck all the Scale boxes.

Blend File
You will move the tube from only the large main section. However when you duplicate it, you will need to duplicate both objects.