Ditto on the half-hurdle drills. What’s the point? You can work on the same aspects in a more holistic way if you stay down the middle rather than the sides.
As for warm up, it is often a question of what’s available. If you have access to hurdles on a warm up track or adjacent area, get over a few 5 stepping or close spaced 3 steps, and then some full speed stuff over 2 to 3 hurdles and maybe a start (block or 3 pt) or two. If there are no hurdles, you do “air” hurdling as suggested. Looks weird, but it works when you have no other options.