I learned how to do it on stock carts from Volcano very successfully, and as far as I know they're not VG. Mine will linger for around 5 full seconds a lot of times, although they are slightly thinner than the ones I blow with a $20-$30 cigar, of course.
PS- I have to squeeze more air out of my throat to make vapor rings look majestic instead of puny. Try this and see if you find any improvements. It took me a whole evening to get the right amount down, because too much will just stir up the air and destroy it. Not to mention, it's a very delicate muscle movement with a muscle group I don't use for anything other than eating generally.