Hi Don,
 
I use umeboshi vinegar, in place of true vinegar.   Its the by product of making umeboshi plums, and is  the liquid collected during the process of making Japenese ume plums.  Plums are sun dried, turning them every day, and then salted and packed with shiso leaf, which is what imparts the purplish color to the plums.  They can also be made with apricots, which is the American version of the process.   The liquid  or "lees" that rises to the top of the barrel is the umeboshi "vinegar".  I've watched and participated in  this process, and I think it would fit paleo standards.    I figure its more paleo than potato vinegar, and is salty and truly sour.  The light pink color  of the "vinegar" could substitute for the sherry color.  Eden has a nice naturally processed   umeboshi vinegar, and there are more expensive brands put out by Mitoku that can be found in Whole Foods, or most health food stores that have a macrobiotic section. 
 The "pickled" plums are supposed to beable to knock out dysentary if taken daily on an empty stomach.
 
Best,
Batsheva
 
 
I'd like to add this recipe: Grilled Lamb Bites with Black-Olive Oil
http://www.foodandwine.com/recipes/grilled-lamb-bites-with-black-olive-oil-cocktails-2007

But it has sherry vinegar in it. This has a distintive taste that isn't going to be replicated with lemon juice. (The recipe already has lemon zest.) I don't want to use grape juice. This isn't an ingredient they should have around. And only 1 teaspoon is needed. Any ideas? Just leave it out?

Don.