+1 on the above. You can also use Decadent Vapours Diablo Loco or Perfumer's Apprentice Jalapeno (http://www.leisureliquids.com/pajalapeno.html). If you don't want the chilli blast either of those will deliver, caffeine also does it - the above are concentrates - if you add them to an existing eliquid - do so only 1 drop at a time into 10ml and let things steep.
A 100% VG juice is hard to come by though as most flavours are carried in PG - www.liberty-flights.co.uk carry a range of VG only juices