I need to run a batch file from USB which will run a second batch file on C:, then allow me to remove the USB media. How can I do this?

I currently have a script that copies a directory on USB to C:, then runs the following line to switch to a local batch file:

call "cmd /c start c:updatepatcher.cmd"

Once the script on C: starts running, I need to be able to remove the USB and do the same thing on the next computer. When I try to remove the flash drive it says that it’s still in use until I close the command prompt that is running from C:. What can I do to fix this?