I'm not sure if this will help, and you might already know this. Maybe some of the more experienced / formally trained guys on here could comment.
there are 2 parts to the biceps (hence the bi part), by changing your grip width, you can influence different parts. flex and feel as you rotate (not bend) your elbow. You'll feel the flex move from the front to the back of the muscle.
When i was going to my trainer, he had me do dumbbell curls with my elbows at my hips, and hands as far to the sides as i could get them as opposed to straight in front of me. also on barbell stuff, i would switch between narrow and wide grips.
went to exrx.net which normally has pretty good info. Although the did not have much on activating the different parts. but they did have a picture showing the different heads.