It's exceptionally hard to create a dom out of vanilla clay, so to speak.

You really can't force him. Perhaps remind him he asked why you didn't come to him in the first place and point out that some of the fear was apathy, rather than rejection.

Have you discussed trying a role play, (i.e., doing something out of character)?
Have you discussed trying a new toy or scene, just in the bedroom?
Have you tried being naked on your knees, arms behind you, clasped as if bound, asking him to let you be of service?

And if you have done those things...

Have you discussed an open relationship?