Current WAN IP range: 100.100.100.0/24
Sonicwall WAN IP: 100.100.100.100
Cisco Router: 100.100.100.1
New WAN IP range: 126.96.36.199/27
You can add a static ARP entry on the Sonicwall but there is an easier method. Simply set a static route on your Cisco router.
# ip route 188.8.131.52 255.255.255.224 100.100.100.100
Then on the Sonicwall, just set up the address objects, NAT policies and any firewall rules that you need.