I would personally not use a fat burner while trying to gain mass. The main point of a fat burner is to expend more calories in a calorie deficit, while trying to "cut". Something like hydrocut may help push your fat loss a little further while you are dieting, but while working towards adding mass, it is only going to be counter productive, eating into calories that you could have used to grow. 

While trying to add mass, you won't be able to help getting a little softer than when you are dieted down, but this is just part of the process. If you want to grow, you have to be willing to sacrifice. Sometimes that means being humble and accepting that you aren't going to look as sharp for a period of time. That doesn't mean that you have to be a bloated mess either though. If you pay attention to your body and understand how to feed it, you don't need to go that high above your maintenance cals, in order to make gains. If you can shoot for 500 cals above maintenance, you should be able to stay fairly lean in the off season. The thing you'll have to watch is that as you grow, you will require more food, just to maintain. Over time, you will slowly need to add more food to keep the gains coming. 

If you find that you need to tighten up a little while in off season, add a small amount of cardio post workout, say 20 min, 4 days a wk. Cardio is good for your overall health anyway and I suggest that everyone does a little in the off season. If you find that you have a hard time eating, cardio also helps with appetite.

So save the hydrocut for your cutting phase and avoid the unneeded stress on your body.