Well, I think you should remove radio commands in init.sqs (or in a mission respectively), depending on player side.
Also because you can't determine who called the radio, you'll have to make West/East commands on separate channels (triggers).
Example:
Make two radio triggers Alpha and Bravo. Alpha will be for West and Bravo for East (as I said before, you'll have to use different channels)
Then put in Init.sqs
if ((side player)==East): then {1 SetRadioMsg "NULL"} else {2 SetRadioMsg "NULL"}
Try to play mission as East/West to ensure that it works, I've never tested it, but it should.
Of course, if you're enabling/disabling radio channels in mission, you'll have to do it relying on player's side again.
Hope it helps (...and works
)