Has anyone flashed an Android build (i.e. a Crespo build) onto a Nexus S phone manually before? How does one do this? I need to find a way to manually add in the system.img file of the Crespo build for Android onto a Nexus S phone.
Has anyone flashed a Crespo build image (I think it boils down to a system.img file) in a way different than the manual?  Such as flashing to the device directly on a Windows 7 machine?

I cannot use the commands as found in the directions at http://source.android.com/source/building.html, such as "$ adb reboot bootloader" and "$ fastboot flashall -w" given that my Android build tree exists on a virtual machine (made via VirtualBox) that resides within a server computer (I can access this via RDP and VRDP, though VRDP isn't quite working at the moment to allow me to use the local USB ports of my remote computer).

(A relevant and linked question I have just asked which is also making figuring this out for myself very difficult and if anyone can answer that one as well that would be helpful:  https://stackoverflow.com/questions/11090473/how-to-get-nexus-s-version-4-0-4-icecreamsandwich-to-register-as-a-device-on)
It's possible to inject your system.img into a previous nandroid backup done from clockworkmod and then restore that backup with the new system.img.

Prerequisites:


Installed clockworkmod recovery
desired system.img saved onto sdcard
do a fresh nandroid backup


To install the new system.img:


boot to recovery
create a nandroid backup to let's say /sdcard/clockworkmod/backup/[currenttimestamp]/
replace /sdcard/clockworkmod/backup/[currenttimestamp]/system.img with your new one
compute the md5sum of your new system.img
update the md5sum in the system.img line in /sdcard/clockworkmod/backup/[currenttimestamp]/nandroid.md5 file with the value from [4.]
restore your altered backup
if needed, do a wipe