These physical problems can be a real bane in meditative activities, but once you get used to the idea of parallel processing, as Tom and others always recommend, they become less and less important. Just regard the physical niggles like swallowing as part of the PMR VR that you know you're participating in, and then get on with what you want to concentrate on for your NPMR experience - just like you can be thinking of what to get for dinner tonight while you're driving your car. I used to take forever getting into what I thought was the 'perfect' state for NPMR experience - trying to get rid of aching neck, getting arms and legs just right, etc, (and I too am constantly swallowing) and often never managing it. With practice and the concept in your mind, you'll manage it simply by shifting your focus, almost anywhere/time. I'm a fidget-bum par excellence, so if I can do it, anyone can! :)
PS. I do find the little mental phrase from one of the TMI H-Plus series tapes "Plus 10, relax,relax" does always help in quieting me down. It still works even after about 25 years since I first used the tape, though of course, you don't need the tape itself after the first couple of listens.
"Life is what happens to you while you're busy making other plans."