You can put this into Guardian > Policy Objects > User Defined > Transparent HTTPS Incompatible Sites > URL Patterns

192\.168\.0\.(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9]?[0-9])




And here's a bit more info about that range:

Address:   192.168.0.0          
Netmask:   255.255.255.0 = 24   
Wildcard:  0.0.0.255            
=>
Network:   192.168.0.0/24       
HostMin:   192.168.0.1          
HostMax:   192.168.0.254        
Broadcast: 192.168.0.255        
Hosts/Net: 254                   Class C, Private Internet