locking and unlocking a drive

Hi all,
I have a problem.
How to lock and Dismount a volume in a drive which has no current partitions
i.e. without any drive letters?

The scenario is:
I have created a partition and formatted (FAT) the same with my own code.
But the NT Explorer doesn’t recognize the partition or assign drive letter
to it until reboot, and Windisk shows the partition as Unknown.
After rebooting everything works fine.
This is because I couldn’t Lock and Dismount the volume without the drive
letter.

Is there any way to make NT assign drive letter to a new partition without
rebooting?

Any Information regarding this would be highly appreciated.

Warm Regards
Anish