Hm. Well, you could spawn {} a script that loops a check to see if the player is within 2 meters of the object at all times, and then have it blow up when appropriate, but I don't know how good that is going to be on performance if you have dozens of the things. Then again I don't know if triggers are any better either - I'd guess they are though, even if they update pretty quickly.
Untested:
nul = this spawn {while {Player distance _this > 2} do {sleep 2}; hint "You're within two meters! Yer dead!"};
Copy-pastable into each object's init field. Will just display a hint once the player is closer than 2 meters to the object. Loops every 2 seconds (make it more or less depending on how "sensitive" you want the IED to be, I guess!). Just replace the hint with whatever effect you want (I'm guessing createvehicle'ing a bomb
)
Good luck!
Wolfrug out.