Gaining

Sooo You're looking for tips to keep up on your size but doing so without being noticed?

I suppose some larger portions, or maybe midnight snacking? Eating what you normally eat but in semi larger portions. Just big enough to stick, but small enough that it isn't too noticeable.

weight gain smoothie. I make a mango one in front my family and no one says anything and also they like the taste of it as well.

Maybe try eating a pint of super premium ice cream every night before bed for a week or two

If you can add 500 calories a day, you will gain about a pound a week, all other things being equal.

That said, it is fairly easy to secretly consume 500 calories. Depending upon your tastes, a few cream-filled pastries would do it. Or a bag of chips. In either case, something you can scarf down quickly while the roomie is out, or perhaps while you are in the bathroom (or she is).

I think you may either have to go for it, or stop. If you try to please everyone, it will be too hard. You don't need to tell your roommate you are gaining on purpose, but you may just want to say that you've stopped counting calories for a while.

Assuming you're not around the roommate 24/7 try all of these tips which are excellent.
My recommended food supplement is Two Cloverhill Iced Honeybuns per day. They're at a lot of convenience stores. Delicious. Available in White or Chocolate Icing.
700 calories each.100% or nearly 100% of the calories are carbs and fats.
Also white bread or rolls with butter. Easy to add a few hundred extra calories a day even in the roomates presence during"healthy meals".