Its impossible to train your lower biceps bro. I hate to be the one to tell you but your under a huge misconception that a # of bodybuilders are under. Just stick to the basics and be sure to get a full range of motion and your biceps will develop fine.
conventional curling movements over emphasize the brachialis which is under the biceps brachi and gives the bicep a fuller peak hammer curls will emphasize the biceps brachi to a greater degree and will fill in the "lower" region.
Rommel- Run a search on that over at anabolics. There's a lot of debate about spot increases from gear; many seem to feel it's the wrong type of oil to stay in the muscle tissue.
I have done some tests and am now a bit confused
1st workout did 8 sets of preacher curls...
2nd workout another day did 8 sets of standing BB/DB curls...
i was sore in the Lower bi's..at the front elbow after the all preacher set.....I little sore just while flexing after the Barbell/DB set......i always figured the stretch at the bottom of a preacher would get the "lower" feel more burn there while on the standing i feel more burn at peack contraction....although i always combine the two now.....