I did some testing today on our MPS 4.0 environment and below are the results.

 Code:
Running "COM1:" "\\Client\COM1:"
Result : No network provider accepted the given network path.

Running COM1: "\\Client\COM1:"
Result : No network provider accepted the given network path.

Running SHELL 'CMD /C net use "COM1" "\\Client\COM1:"'
Result : The operation completed successfully.


Does the SHELL command works for you also?