IPSec server issues behind a netgear FVX538 with NAT

Hello.

Is it possible to get L2TP/IPSec to work with a securepoint VPN server / Firewall when the outgoing interface of the VPN server (Securepoint) is behind a NetGear FVX538 router and hence on a NATed private IP?

I have got PPTP to work but this is not really secure enough.
I got this to work by enabling PPTP, L2TP and IPSec passthrough on the Netgear router to stop it messing with the traffic (This is for outgoing though is it not?), and by forwarding the PPTP service to the internal private IP of the securepoint system.
NB: I believe securepoint is using openswan. (but i cannot configure it directly)

The PPTP service consists of protocol 47 and TCP port 1723. (NB: The PPTP service is preconfigured on the FVX538, and as such i do not know how to configure the fireway for protocols other than TCP/UDP)

For L2TP:
I have forwarded UDP port 500 for Internet Key Exchange (IKE) traffic, UDP port 1701 for L2TP traffic, and UDP 4500 to the securepoint unit.
NB: outgoing access is unrestricted.
I do not know how to open up protocols 50 and 51 on the FVX538!
(NB: I have other permanent native IPSec tunnels terminating on the Netgear)

NB: I also have a bunch of static IP's, and so the permanent IPsec tunnels terminate on one public IP on the netgear, and I have the netgear firewall forwarding all the above mentioned ports etc to the securepoint unit from a different desination public IP.

NB: I have also tried connecting to the securepoint unit from inside the network and its all thumbs up!

Thank you in advance :o)