Dowatch, dofire, etc are all nice and good, and with them you could get some grunts to shoot rounds into some bushes or whatnot, but there are still big problems with OFP itself that would be very difficult to get around.
Basically, the point of covering fire/base of fire is to get the enemy to keep his head down, while the rest of the squad flanks him, and then assaults through his position (with bayonets/grenades and some war cries). Now, in OFP, the enemy doesn't stop shooting at you just because you are shooting at him. Nor would he stop if you were shooting at some game logic near him. The only way to do this would be via scripting the enemy to stop shooting.
But now we come to the other problem. The only reason the enemy would stop firing is if he was ducking into his fighting position. Unfortunately there is very little hard cover in the OFP landscape, and the AI doesn't know how to use the little that is there. A bush is NOT a fighting position. I dont' know about you, but if someone was firing at me, and there was nothing I could get behind that would stop those bullets, I would put as much lead in the direction of the bad guys as I could. I would NOT simply stop firing and wait to get killed.
So basically, if you wanted to do this, you could, but it would require a lot of scripting (such as having the enemy lay down behind his sandbag walls when getting shot at), and thus it would be hard to make this into a universally useful script. It would only be useable in a carefully constructed situation.