I used the same recipe you linked to the end of March. I made 2 batches both slightly modified.
Batch 1: I scaled the recipe to 1 gallon and used all lemonade, no limeade or pink lemonade. I also added 1/4 tsp of baking soda to cut down on the acidity, airlocked it and left it alone in a dark cabinet and everything went smooth, no smell, and it's already bottled.
Batch 2: I made the 5 gallon batch, again all lemonade and 1tsp baking soda and I reduced the sugar to only 4 cups for the whole batch since I wanted a lower alcohol content and I used 2 packets of EC1118 instead of the Montrachet because I was afraid the 5 gallon batch would have trouble getting started with the Montrachet. This batch had the very bad sulfur smell!!
Batch 2 fermented in one week down to 0.994 on 4/8. I was unable to rack it until 4/12. I racked it into another bucket splashing it from up high to try to aerate out the smell. Then I took a stick blender with a whisk attachment and whisked the whole batch and airlocked it. Did some reading online that night about the sulfur smell and on 4/13 decided to open the lid back up and we poured the lemonade and back and forth between 2 buckets SEVERAL times to aerate it even more. Airlocked it. Then I got to thinking that any sulfur that got released would just get trapped in there so I removed the airlock and hooked up my foodsaver vacuum to the lid to suck out the air. I did this once on 4/14 and once on 4/15 (I guess removing the lid would have done the same thing but I am a newbie and was afraid of oxidation if I didn't get the air out of the bucket because there was no more fermentation). I let it age airlocked in the bucket for 2 more weeks and checked it again and a slight smell was still there but just barely noticeable. I whisked it up again with my stick whisk and airlocked it. A week later checked on it and the smell was gone. I racked it onto sorbate, k-meta, and some more cans of lemonade concentrate and then ran out of time to bottle so it's sitting in a carboy right now but there is no smell other than lemon.
On another note, when we first racked it and it had a horrible sulfur smell, we racked 1 qt of it into a pitcher for taste testing. Added 1 can of frozen barcardi strawberry daiquiri concentrate mix to it. Left in the refrigerator with the top of the pitcher vented and within a week the smell was gone too (I did shake it up several times a day to help release the smell). My fridge didn't smell very good all week but it worked!!
I would not give up on yours. Maybe pour it all back into a bucket and whisk it every day until the smell goes away. I was too chicken to play around with adding copper sulfate. I can't guarantee the whisking will work for you because I started treatment about a week after the smell, I don't know if having it in the lemonade for as long as you've had it there makes it harder to get rid of or not. Good luck!!