Stretching is definitely where its at. I've been cursed with an abnormally sized head and i rarely have any issues, unless of course I forget to stretch. I'll usually just sort of pull my head down towards my chest with my hands firmly, then while keeping the pressure on I'll sort of roll from side to side, making sure to also pull towards my shoulders. I'll usually just do this for about 20 seconds or so after my rig is set up and they're line checking the other guys in the band.
Also, if you're on tour and you're stretching before each show, any soreness will likely be gone by the 3rd show. In much the same sense that you can drink a hangover away, you can also headbang a bangover away. Though I usually call it gig neck.