I understood this situation very clearly.
FastCopy Shell extension runs in explorer as normal privilege.
And it uses CreateProcess("fastcopy.exe") with pipe(as stdin) for selected/dragged files information.
But creating process *.exe that requires admin privilege, it requires admin privilege, so it will fail.
To elevate admin process, it can't use CreateProcess, but it can use ShellExecuteEx("runas") hack. but it can't pass pipe(as stdin).
So, to resolve this problem, it requres to modify "passing selected/dragged files information mechanism", and it is not very easy :-)
In the future, it will be implemented when the shell extension will be required to modify for other big futures.