OK, so, as I mentioned above for something like this, one possible answer is to use the CCLens3D class to get the "effect" of magnifying something in a circular manner.
I found using this to be a little tricky because it doesn't seem to work unless it's a child of the top level node of your 'scene'.
Here is some code I use to create a lens that moves around the screen, and then disappears:
// Create the lens object first.
//
CCLens3D *lens =
[CCLens3D actionWithPosition:fromPos
radius:50
grid:ccg(50, 50)
duration:2.0];
// Set the "size" of the lens effect to suit your needs.
//
[lens setLensEffect:1.0];
// In my case, I then move the lens to a new position. To apply an action on
// a lens, you need to give the actions to the actionManager in the
// CCDirector instance.
//
CCMoveTo *move = [CCMoveTo actionWithDuration:2.0 position:toPos];
// I had another action in this array, but this will do.
//
CCSequence *seq = [CCSequence actions:move, nil];
// Now tell the actionManager to move the lens. This is odd, but it works.
//
[[[CCDirector sharedDirector] actionManager] addAction:seq target:lens paused:NO];
// Now just for some more weirdness, to actually make the lens appear and operate
// you run it as an action on the node it would normally be a child of. In my case
// 'self' is the CCLayer object that is the root of the current scene.
//
// Note that the first action is the lens itself, and the second is a special
// one that stops the lens (which is a "grid" object).
//
[self runAction:[CCSequence actions:lens, [CCStopGrid action], nil]];
I imagine that you should be able to stop the grid by running the CCStopGrid action when you want to. In my case it is a programmed thing. In yours it might be when the user lets go of a button.