There are people putting on 10 lbs a year at ~10% bf. Not staying in stage condition. But not fat. You've seen Justin do it with Paul Barnett and Ben Pollack. Justin's younger guy that just lost to Sam sulek, Cole Albersworth has done it the past 4 years in a row.
If you want to put the absolute most muscle on in the shortest period of time, you might need to get softer than you desire. But unfortunately, it's usually not eating junk. If so powerlifters and strongman would like bodybuilders. How much clean food can you eat before you're just sick of the whole thing?
There are guys who do it.
It can be done. But there's no secret. It's living like you're on prep, year-round. Cardio. Training. No missed meals. No binging. Why don't most people do it? Because it's fucking hard.
Yes, it requires drugs. I don't believe it requires a gram of tren. If you think a gram of tren isn't any more risky than a gram of testosterone, you can try it. The reason that competitors pick less harsh compounds in the off-season is so that they can push the dose with fewer side effects.
The first thing to do though, is get in shape. It's not a mini-cut. Get in stage shape. All the rebound strategy conversation is months away. If you're 15% bodyfat, it might take 24 weeks. But the fat has to come off. Good luck.