Aside from all the pushback you're already getting... that the Rangers wouldn't consider trading him... it's pretty standard practice for NMCs to go into effect when the extension is signed, rather than when the contract goes into effect on July 1 in a typical year. This is for UFA contracts only, obviously. It's different when there are RFA years. In other words, I'm pretty sure the NMC is already in effect. Players want it for this exact reason.
Someone correct me if I'm wrong, of course... I just seem to remember seeing that several times.