OK, kindergarden celery experiment aside, I'm going to give my serious response here.
First of all, I've never actually tried flavoring marijuana this way, nor do I have any interest in doing so. If I'm going to be smelling marijuana (let alone smoking it), I think I'd like to smell what the actual herb smells like, not some added flavoring agent. It really ought to smell and taste pretty good all by itself!
You don't take beautiful $25/lb Hawaiian Kona coffee, then add artificial hazelnut to it, do you? Would you take a nice 14 year old Scotch whisky then add it to RC cola? How about taking a $25 Dominican Cohiba cigar and then dipping it into cherry cough syrup? So if you wouldn't do those things, why are you going to take your $300/oz homegrown connoisseur herb and soak it with Welch's grape juice?
If I want to taste some grape juice, then I'll just drink some, preferably a nice Chardonnay from Napa, fermented then aged in oak for five years, thanks. I wouldn't want to take a chance ruining good cannabis with kiddie flavoring tricks.
Next, I believe adding grape juice to your grow is just fundamentally a bad idea. Grape juice is basically just a concentrated sugar solution. Add that to your soil, and you're potentially going to cause all sorts of problems with bacterial and/or fungal growth, attract insects or other pests, and even potentially damage your plants roots.
Unlike the cut celery experiment, plant roots act as biologic membranes; they don't just instantly take up any liquid they're surrounded with. Flavoring agents (actually smell agents) are generally large organic molecules, and without good evidence to the contrary, I'd assume that even if added to soil, the plant roots simply wouldn't absorb them. They'd absorb the water from the grape juice, but not the smell.
Also, plants have metabolisms. Any flavoring agent that did get taken up by roots would probably be metabolized by the plant relatively quickly and effectively destroyed.
Now, if you really wanted to get your grape juice into your buds, you MIGHT be able to do that if you cut off the plants stem at harvest, then immerse the cut stem into (say) a whole cup of grape juice for about 3-4 days. A little light at the top would ensure the plant would transpire water vapor out, and then take up your grape juice via capillary action through the cut stem, just like the food coloring in the celery experiment. Most of the grape juice would probably go into the plants leaves, though some probably would get into the buds.
Even so, again, grape juice is mostly a concentrated sugar solution. So while you may have gotten some smell/flavor in, you've also filled your buds with sugar, which once dried will caramelize when burned. Not sure I'd want to smoke that.
Might was well just take your cured (or uncured) buds, and just soak them in grape juice then redry (or cure). Seems easier to me, and probably more "effective", even if this is like dipping your expensive cigar into cough syrup.
In short, I believe that adding grape juice to your plant's medium probably will NOT cause it to be taken up by the plant, and it might even hurt the plant. Adding it to a container with CUT plants for a few days might let it get taken up into the leaves and buds, but even if this were to happen, I'm not sure the result would be worth the effort.
not much of a convo 
