Another thought -
If, indeed your expander is locked on the threaded bolt and is under compression, perhaps just a long-shafted screwdriver would do the trick. No need to hold the "nut".
Try this as a demonstration: Take your good pole apart. Tighten the expander against the bottom section to simulate the frozen one. Now, hold the expander with one hand and with a screwdriver in the other hand, "tighten" the screw, moving the "nut" away from the expander.
Got it? Now go find a long rod you can grind down, and drill a hole through your handle.
Or send it back to Grant.