Anyone experimented with J-lube?

I love probe thick and rich lubricant, and, while it's cheaper than other lubes, if you're using a lot (and I do) then it gets pricey. So I finally decided to buy some J-lube powder and make my own. Simple enough, 1) mix powder with warm water 2) lube up 3) profit enjoy. Now here's where things, if you'll pardon the pun, get sticky. The stuff goes bad in my hot, humid, southern climate pretty fast. I don't want to freeze it and have to wait on a thaw, or keep it int he fridge (I don't like 45 degree butt lube, thank you), so I thought--let's add some kind of preservative.

The most logical thing, to me, seemed vegetable glycerine. I learned the messy way that this isn't a great thing to put up your butt, unless you're constipated. Not me, I'm trying to get stuff IN.

So I read somewhere online about using grapefruit seed extract as a natural preservative. The problem is, I have no bleeding idea how much to use in relation to water and the powder to make, say, a 9 ounce (reusing an old lube bottle) batch.

So I thought, there's some smart guys on the Aneros forum, and one of them is bound to have thought about this before. So I put it to you, gentlemen, what can I use to stabilize my awesomely cheap and amazingly slippery J-Lube so that I don't have to mix fresh batches all the time?

Thanks!