I have found a few examples of Cross vCenter vMotion posted on the web that can migrate when the virtual machines are using standard vSwitches. I built this workflow to perform the migration when the virtual machine is attached to a DVS. If you are going to give this a try you will need to provide a couple of usernames and passwords in the general attributes and please take a peek at the code and see if things are going to match your environment. This is working well in my environment and your millage may vary so please look before you leap.
If you make any enhancements, please share your updates with the class 
Cheers and enjoy
Steve