Isn't this a form of hairpin NAT?
There is no 'one command' in ScreenOS to configure this. But, you can achieve it with a couple of policies and NAT statements.
This might help to get started: http://forums.juniper.net/t5/ScreenOS-Firewalls-NOT-SRX/Why-is-a-global-zone-policy-required-to-hairpin-NAT-MIP-from/td-p/243810