No. Absolutely not.
You would have to have a "real" IP from a different subnet (maybe split the IP Set you have if it is large enough) and then create a Tri-homed DMZ by adding a third Nic in the ISA and properly configuring a new perimeter Network in the ISA to work with that set of addresses. You would then have to set the Network relationship to "routed" between the External Network and the new DMZ Network. Then create an "allow all outbound traffic" rule that goes From: External,...To: the IP# of the specific machine.
But without going through all that,...the answer is "no way,..not gonna happen".
If this machine needs direct access from the Internet so bad then you can just duel-home it with a second Nic and rig it up with an internal and an external nic and place it on the network edge (indentical to how the ISA is setup). This would be plain horrible from a security perspective,...but is essentially the same thing as what you were asking to do in the first place.
