This is an idea I passed along to another filmmaker, and though she did like it, she charged way too high a price for the work. So I decided to copy and paste it here for your delectation:
You and your boyfriend (pov) are in a room chatting about your height when he notices something poking out from under your shirt, what appears to be a pull-cord in your belly button, like from an inflatable life raft. You question what it is and how it got there, but before you can tell him to leave it alone, he pulls it out. Then there is a hissing noise, and it gradually gets louder. Then your body starts to grow taller, and then the shot cuts to your arms and legs getting thicker and more muscular. But just as you're showing off how buff you're becoming, you're boyfriend points out that your breasts and belly are becoming thick and plump as well. By the time it's over, you're standing at twice your normal height, looking like a bodybuilder that swallowed a life raft. You debate your new body with your boyfriend for a few minutes. For everything you don't like, he loves as he turns out to be a bit of a chubby chaser.
Optional extra part: After a couple of minutes of convincing you, the boyfriend spots what appears to an emergency blow pipe on your body. Without hesitation, he grabs it and starts blowing in it, causing you in small burst to grow taller, thicker and more bloated. Soon enough your cheeks start to fill so you can't warn him how tight you're getting. And eventually, you pop are found lying at the floor shrunken back to normal size.