Substitute for wine? I am cooking for someone who does not eat dishes that have been cooked wine. What substitution would you suggest?

The author says it is only to enhance any sauce made to serve with the meat- so you could easily forego the baste entirely. It certainly isn't done to benefit the meat in any way, because basting would never get through the skin or fat layer. I wouldn't substitute a thing. If you must baste, use the fat drippings rendered from the pork itself. Basting doesn't do much except lower the oven heat periodically, not a benefit to the roasting process or the meat.

In the recipe headnote the author flatly states that the wine basting is untraditional.

Even if I had grape juice in the refrigerator, I wouldn't use it. It has a considerable different flavor profile than wine and is also full of the sugar that hasn't been converted to alcohol by fermentation. Regular grape juice isn't made with typical wine grape varietals either, another strike against that.

I'd go the most traditional approach and make the roast without basting with wine.

I'd just skip the basting altogether. The NYT has a similar recipe for a porchetta-style pork shoulder (https://cooking.nytimes.com/recipes/1017068-porchetta-pork-roast) and there's no basting involved, just the rub. And looking at pork belly porchetta recipes, it doesn't seem to be a traditional or necessary step.

High quality, lower sugar grape juice, white peach juice or pomegranate juice.