There is no way under the current system to apply a buff when a user logs in. It has to be through the interaction of a skill or item.
The npcs buff players by consuming an item on the player. In the case of Primo D Buffer hes forcing a set of +7 stat food on you and watching you eat it in front of him.
Or you can change the VIP buff to persist through death, like what happens with Reno buff. That alone would make a HUGE difference
Thats what i said , doing this shouldn't be hard