Very simply, you can't. Unless those two toms were not being used in the first place, which may very well have been Lars Ulrich's reason for shedding them.
But more realistically speaking, it's possible that he simply wanted to create a different sound. Many musicians agree that sometimes you can make your music better by limiting your resources. For instance, arrangers decide which instruments they'll use before starting to arrange a song, and then they'll adapt the song to this limitation they have imposed on themselves.
In drumming, it can be similar. I'm guessing that Lars Ulrich wanted to experiment with a completely different sound, by using a more limited drum kit. Of course, he'll have had to adapt his parts in all songs so that they'd work this way.
If you'd like to hear to what extent you can make a drum kit sound different by removing pieces, I suggest you have a listen to Alt-J's album, called An Awesome Wave. The drummer doesn't have a single cymbal other than the hi-hat, and also makes very limited use of his bass drum. In my personal opinion, it sounds very unique.