If you're building a whole jig for this, you could fix a pillow block to the motor end of the jig and then have a sliding or adjustable pillow block mounted on a piece of dovetailed wood or aluminum. All you'd need is a couple of toggle clamps to latch it in place. That way you could slide the rod into the fixed pillow block, slide the adjustable one over the end of the rod, and clamp it in place. Once you were done winding, just unclamp the block and remove it from the rod, allowing the whole rod or just the wire to be removed. For the smaller rod, use an 1/8" adapter sleeve to pair it up with the bearing ID on the motor end, and build a second adjustable block with a smaller bearing ID so you can easily remove the wire from the rod after you're done without pushing it over a sleeve and potentially messing up your coil. Point to note: make sure the center points of the bearings are at the same height from the mounting surface, or it'll get weird real fast when you start winding.