"This IP has to be known by the GW and access has to be granted." I am not sure that this is an accurate statement.
The SecuRemote connects to the gateway identifying itself by the public IP of the router/gateway it is coming from.
I do not think that the GW should be in any way aware of either the public IP or the private IPs assigned to the SecuRemote clients.
I do believe that major limitation of SecuRemote is the lack of support for multiple clients (or concurrent connections) originating from behind the same public IP.
If I am wrong, please do correct my assumptions.