I dont know it exactly but i dont think this is possible.
you can create a backups with 91mobile pc suite :
91 pc suite for iphone
i use it on my own caused by the fact that i never use a backups
iam not abled to tell you if that works proper.
But there is an app called Pkg-Backup wich is maybe interesting for u:
How to Backup Cydia Apps | How to Restore Cydia Apps | iPhoneHeat
I hope this helpz u ...