MGMakeStretchy

Stretchy bones:
2 threads:-
available in this long thread: HERE
BUT also has own thread: HERE

This does as below, nothing you couldn't do in LW using expressions, but much easier to set up....

Usage:
Select any objects or bones which you may wish to make stretchy (able to scale them in the x/y/z whilst it's children remain the same size)
Apply the generic plugin MGMakeStretchyGN.Now you can use the Stretch tool on the items, without this affecting their children.

How it works:

This will add a child bone to the item, and apply the Motion plugin MGStretchCompIA to it, which compensates for any scale modifications done to
it's parent. It will also reparent the stretchy item's child to this new compensator bone, so they won't be affected by their parent. It also hides
the compensator bone and locks it from selection. If you want to adjust this bone, use the Scene editor to select it.

MGStretchCompIA has toggles for X/Y/Z channels,so you can switch them off individually if necessary.