General

I'm not entirely sure if that's possible. The quickest results mean you need a LOT more calories, which of course means you'd have to eat a lot. You'd have to stuff day after day, and that's not feasible for most folks.

That said, there are small changes you could make to add calories. Any one of these alone won't make a huge difference but together, they can. Here's a few examples:

Cream and sugar in your coffee. Extra mayo on your sandwiches. Extra dressing and cheese on your salad (you always do need your vegetables, even if they come on a burger; delivery method isn't that important). Rediscover candy and cookies, snacking on them when you can. Something you don't have to refrigerate so you can keep it in the car. Try some extra butter on things that use it. I think you get the idea.

Enough small changes day after day will add up, and will be important to ensure you don't lose as you increase in size. In essence this is the opposite of the advice for weight loss of making small substitutions and changes to reduce calories.

You don't have to adopt all the examples I said, and there's countless more of these simple examples. You may find yourself adopting and preferring some of these. But if you don't like one, don't do it. That's when you have to use discipline, determination, and force yourself to do it. That will cause more burn out.

At least you're a pretty good size already, so you're already past the hardest and most difficult part.

Snacks!

At first it might behard to remember to snack, but it likely won't take your body long to kearn tbe schedule and to stsrt reminding you with hunger prompts when it is time. Plus certain activities can be a cue to snack.

I don't know your schedule and life, but just for example.
- breakfast
- a snack in the car on theway to work (say 2 poptarts, for about 400 calories)
- 10am have a coffee with plenty of cream and a muffin (probably another 400)
- lunch
- 2pm a bit of chocolate (200 calories)
- 4pm a piece of fruit (50 calories)
- on the drive home a couple more pop tarts (400 calories)
- supper
- 9pm another snack, say a bit of ice cream (250 calories)

None of that is very time consuming, the only part that might seem odd to others is the poptarts but that is in the privacy of your car, and it adds up to 1700 calories in snacks. Personally I find it easy to end up snacking even more than that once I'm in that mode of eating something every couple of hours.

That much snacking can suppress your appetite for meals, but that is when you need just a bit of willpower to make sure you eat something like your normal meals.

Good luck!