Is it possible to make my belly look like I am pregnant without being pregnant?

Interesting question.  This is a difficult question to address without photos.  It would be nice to see a photo of your navel.  In addition photos of navels that you feel are more pleasing.  Please send photos.

What you are asking doesn't involve common surgical procedures and it would be difficult to find a surgeon that can help you achieve your goal. Perhaps a plastic surgeon is not what you need. Weight gain may be your best option for now, and then when you have enough fat density on the abdomen, then probably a procedure or two may be done to contour the belly. 

I'm not sure anyone can give you the results you are looking for.  Women are only pregnant in appearance for 7 months during their pregnancy.I feel you have some issues which you should discuss with a professional prior to seeking out a plastic surgeon who may not be able to give you what you desire.

My first thought is that your desire to look pregnant as an emotional one and the treatment is also emotional. I do not think anybody should or would offer surgical intervention to create a pregnant look. For those who carry excess intra-abdominal fat or a predominately Intra-abdominal fat distribution becoming Obese is probably the closest resemblance. Since most genotypical males tend to have more intra-abdominal fat simply gaining weight would accomplish this To some degree. It would however give you the look of an overweight man with a Beer belly rather than a pregnant woman which are quite different. I don’t believe anybody looks good being overweight so I wouldn’t recommend going that route. I don’t think anyone has a good outcome with the exception of using prosthetics which is probably your best option.
Best, 
Mats Hagstrom MD