Sorry, I don't get it to work.
Please let's explain my situation:
- SSG5 directly connected to the internet on ethernet0/0
- Two VPN-Tunnels, one with 172.16.x.66/30, second with 172.16.x.70/30
- ethernet0/2 connected to my DMZ with 10.x.x.165/28 (on bgroup0)
- The internal server has IP 192.168.x.10/24
- My partner company will connect to 172.16.x.74/29
I've created mip for 172.16.x.74 to 192.168.x.10 on bgroup0 but that doesn't work. You example with loopback.1 does'nt work either, but I think it's because I miss-explained my goal 
I don't unterstand the concept in that case...