Load up the Chinese Embassy level
(The 2nd trip between Slaughterhouse and Presidential Palace)
You start off with 5 grenades
Start off by opening the door to the Chinese restaurant and take out the first light (not lantern)
This gets the attention of the guard(s)
Throw your grenade and hopefully take out 2 guards
save the game then exit to main menu and start the level fresh, then repeat till the trophy pops.
This way your progress is saved, if you just reload it wont save progress