1. Start MC outside business
2. Get in and shut down business
3. Get out and disband MC
4. Get in (without starting MC) , use NB to start business, do resupply, shut down business again
5. Disband MC inside and go out
6. Go to story mode and back be online
7. Wait outside the business for LJT's message of resupply (~10 mins)
8, Received message and get in (without starting MC), use NB to start business (supply need to be 100%, if not, do step 4 and 5)
9. Disband MC inside and go out
10. Wait for 15 mins, start MC outside business, you should get the message from LJT about staffs coming back.
11. Get in and disband MC inside the business, go out and be back ~10 mins (without starting MC)
12. Profit...

---- IF THE ABOVE DOES NOT WORK, YOU CAN TRY THE WAY BELOW, BUT MOST OF THE TIME THE ABOVE SHOULD WORK ----

Additional info, how I do it (steps from yupiec's method):
* I use a public solo session.
* In step 7 (yupiec method) I additionally leave the area and go watching the securitycams of my bunker, and after receiving the message about the supplies I give it another 2-5 minutes before doing step 8.
* In step 10 I start an organisation and do some vip work (I use fortified, because you can leave the boxville alone and leave the game idle), and I give it another couple of minutes as well before starting the MC.
* In step 11 I do more ceo work or bunker supply missions (as a ceo), selling a car from vehicle warehouse or reorganizing my garages