Become "Invisible" in trigger zone

[Blackjack_UK]

Hi,

I've got a moving trigger attached to a train, and want to simulate using the train's radar return to mask a helicopter if it's inside that trigger zone.

Is that possible? And is it possible to just make it radar invisible but still allow visual and IR aquisition? Ideally both of those would be a little degraded, partly because of the train and partly because of the WTF factor.

Thanks