I rarely have a problem with this...
Powder, a little air in the tube, tube in tire, start with one bead and the valve stem set.
Usually people can get the second bead most of the way on, but there is that final
stretch of a few inches on the 2nd bead that they cannot get over.
Set the tire lever so that you can apply pressure to the bead,
and pinch the beads together all the way around the tire.
As you do this the bead gets pulled into the center deeper portion of the rim,
and off of the shelf that makes up part of the hook bead by the tension of the lever.
This gives you more "slack", kinda like the installation of a UST tire.
As you pinch you will feel the lever loosen, but you must keep a little tension on it until you get back to the gap.
Usually you can just pull it over with a thumb after that, or hold the bead and run the tire lever towards it.
The most difficult rim/tire combinations around are at least made manageable with this trick.