Default [Q] IS701R unlocking bootloader problem

I have Android 2.3.3 bsnl penta is701r tablet, which was rooted using framaroot. Now i want to upgrade new rom but the problem is that i cannot find any way to unlock bootloader as this tab is usb locked which does not allow my tablet to be connected with pc. i used edit default.prop but everytime it is loaded bu default parameters after reboot. also this tab does not have volume keys which most of the post suggest during updating rom.