On Wed, 13 Jan 2010 22:20:53 -0800, Godspeed wrote:

That's an interesting idea! I hadn't thought of putting a bladder in. Seems
to me that just might work. If they exist.

Check local codes, especially fire protection codes, to see if it's legal
to add a bladder which could melt in a fire and which would have to have
openings for the valves.