The morph will change instantly, reflecting the new calculated value. If that doesn't matter, no big deal. Otherwise, you can control the morph with multiple dials and probably accomplish what you need. For instance, if you wanted the morph to start applying at twice the rate at some point during the bend, you would duplicate the master channel (give it a new name), but set it so it didn't kick in until the rotation was at the value you wanted the increased rate to occur. Obviously, the two channels would need different min values. The advantage with this method is that no pose file is needed. The effect when the second master channel kicked in would be constant.

The above technique is also useful for reversing a morph after the rotation reaches a certain point -- the rotation continues, but the morph starts unmorphing.

I probably invented a word in there somewhere. Oh well...