pygtk - scale widget events

[ch424]

Hi

I'm trying to make a zooming in/out slider, but I want to make it
re-center when I let go of the mouse button on it -- i.e. it starts
with a value of 1 (in the center of the slider), then the user can drag
it to the right or left, while it does UPDATE_CONTINUOUS, but when the
user lets go, I want it to go back to 1 (its center value) again.

So, basically, my question is: Is it possible to make a scale widget
with UPDATE_CONTINUOUS reset to a value when the user releases the
mouse button on it?

Many thanks for any help,

Alex