The effect you want is to allow the smoke particles to last longer before they disappear. The BIS grenade is pre-scripted. Therefore, without creating a mod for the game, the BIS grenade cannot really be tweaked or such.
There might be a work around with some scripting. Attach an event handler "fired" to the "thrower". The script should detect if the thrown object was a smoke, and if so, use a nearestObject player to find the thrown smoke. Catch the smoke .1m above the ground, and setPos it to something like [0,0,0]. Then, using a script generate your own smoke on the position that you caught the smoke.