Several years ago someone asked the same question about why their mock orange hadn't bloomed after 3 years. Here was the answer:

"Best flower will be accomplished if the plants are in full sun. Are they shaded more than a light shade?
Have the plants been pruned? If they are not pruned immediately after flowering, the flower buds for the next year may be pruned off.
Are the plants planted in a wet site? If they are, they will fail to perform as expected. The lack of flowering could indicate a plant that is not thriving because of poor site selection."

In addition mock orange doesn't usually need fertilizer. Fertilizer can cause the plant to grow a lot of leaves without setting buds.

It's still early enough in the season for you to transplant your mockoranges to an area better suited for them. Mockorange should be pruned in the spring after blooming so that it will set blooms for the next season. Once they are established you can cut approximately 1/3 of the old canes to the ground which will encourage new growth from the ground. Never cut back the tops of the canes.