Let's say you want hosts 101 and 102 to bypass the VPN.
#/etc/config/network
config rule
option in 'lan'
option src '192.168.100.101/32'
option lookup '100'
config rule
option in 'lan'
option src '192.168.100.102/32'
option lookup '100'
config route
option interface 'wwan' # <-- make sure this is the correct logical wan interface name
option target '0.0.0.0/0'
option gateway '192.168.1.1'
option table '100'
# This is to avoid some unwanted side effects
config route
option interface 'lan'
option target '192.168.100.0/24'
option table '100'