Just try the VG and see if it helps. I have been vaping 2 years and still get a negative reaction if I vape something with too much PG. I seem to be able to enjoy some flavors that are 30-40% PG, but even then I have to alternate with a 100% VG flavor or my throat gets irritated.
Also I notice on the times I have switched from smoking (I had two smoking relapses in the last 2 years) to vaping I tend to cough a little more the first day. The vapor is just different than smoke, and maybe since it is moist it starts to loosen crap in the lungs and stimulate coughing. But this goes away. Tell him to take slower, smaller drags until his lungs adjust.
Oh, yeah...and he needs to make sure he has a beverage to sip while vaping, and needs to drink plenty of water.