Will applying fenugreek oil make my breasts bigger?

Creams and herbs will not work, save your money.Not many good choices to have larger implants without surgery. You can research and try "BRAVA" suction device, or gain weight (not advised). Hormone pills such as Birth Control Pills in many cases will result in a modest increase but is not predictable.Surgery is the most dependable and predictable method using implants or your own fat.

I know of no studies that show that rubbing fenugreek oil on the breasts will make them larger. 

Unfortunately, you've been misinformed. Massage, oils, creams, and pills are ineffective for enlarging the breasts. The only effective, reliable, and safe way to increase the size of the breast is through breast augmentation. If this is something of interest to you, you should consult with a board certified plastic surgeon who can answer your questions in greater detail and evaluate you in person.