Thanks for your response Shaun. I started with that article first, before posting my question here. Unfortunately, that doesn't provide a desired solution.
CLIENT_ACCEPTED gets triggered only when the VPN client is connecting to VPN VS, but not after the VPN client is already connected and has the VPN IP assigned from the pool.
LB_SELECTED doesn't get triggered at all, since there's no back-end server assigned to a VPN VS.
So, unless I'm doing something wrong, the above link doesn't provide the expected result.