Scaredy-rattie.. some help?

[Tizzrah]

I have a question about one of my boys that is making me quite frustrated.  He's about three months old, and has been with me for two of those three months.  I got him with another male from the same litter.  The other male, larger and obviously more dominant, is very friendly and inquisitive and enjoys coming out of the cage to play.  Zenith, my scaredy-rattie, is only comfortable in his cage.  I've tried coaxing him out with food, but once out in the open, he freezes for a moment, and then darts right back in to cower in the corner.  If I take him out (both alone, and with my other boy), he gets very tense and barely moves at all, only shivers in fear.  This has been going on since I got him.  I don't know how to make him more confident and to relax when being handled.  

Can anyone please help?