There are a few ways to do it:
1) Set SB-800 to SU-4 mode (press/hold Sel, navigate left, select SU-4, non-iTTL method)
2) Get a SU-800 and set up SB-800 to do CLS (press/hold Sel, navigate left, select Remote, sync the channel/groups, i-TTL/CLS)
3) Get another SB-800 and set up SB-800 to do CLS (press/hold Sel, navigate left, select Remote, sync the channel/groups, i-TTL/CLS)