Normally, a thinner juice will produce less vapor and adding "vodka" to your juice will cut down the amount of VG as well as flavor, nicotine and PG.
If you are just looking for more vapor your best bet would be to get some VG and add a bit to it, just experiment with it and see what works best for you. However, you will have to go up a bit on your nicotine level and possibly add extra flavor to your liquids, because you will be diluting your juice if you add VG to it.
Hope I was able to help, if you have any questions feel free to send me a PM.
Jon