Tried today- got two stars then sheparded police into that underground parking lot, the one with the two vending machines. Police came in and were bottlenecked along the drive. Try as I may, I could never get the wanted level to six. Got it to five for a long time, lol.
The best way I find to get six stars is to simply go into a locked island. If you aim to get six stars without doing the option above, don't stay in one location, move around the city racking up the kill count on peds and cops whilst causing mass destruction, that should aggravate the cops enough to raise your wanted level.
You really have to be killing the Noose (Swat) or FIB (FBI) guys to get up to 6 stars I think. When the Noose do finally show up, nick their van. It's bullet proof so you can surive for ages in it. Or find one of the Gruppe6 trucks from the start as that is armoured as well.
A shortcut is to go on the Internet in the game and go to www.littlelacysurprisepageant.com (either by typing the URL or clicking through LuckyFind Search until you see the link), which alerts the LCPD that you attempted to view explicit images of child beauty pageants and gives an instant five-star wanted level when you log off. Then you don't have to fight as much to get up to six stars.