[shavit]

That works too, confirmed;

/**
 * Sets the Base velocity of an entity.
 * The base velocity is the velocity applied
 * to the entity from other sources .
 *
 * @param entity        Entity index.
 * @param vel            An 3 dim array
 * @noreturn
 */
stock Entity_SetBaseVelocity(entity, const Float:vec[3])
{
    SetEntPropVector(entity, Prop_Data, "m_vecBaseVelocity", vec);
}

/ smlib