I've only tested this on the WoWBeez Battlegrounds realm, so it might work in different servers too.
Next time you buy any poisons from the vendor and apply them, instead of buying them / reapplying them, just relog or change an area, IE - in the battleground realm, either relog or enter / exit a BG.
The timer on the poisons won't be reset all the way, but they will go up about 10-20 minutes, (dunno why). Congrats, now you don't have to waste gold on poisons again!