Using IP Helper addresses, one router serves the entire network. IP-Directed broadcasts will assist in the decision to know which scope to provide the client.
On the router that serves internal addresses, here are two of many possible scopes
ip dhcp pool DOT96
network 192.168.1.96 255.255.255.240
dns-server 68.10.16.25 68.10.16.30
default-router 192.168.1.97
lease 7 23 59
ip dhcp pool DOT64
network 192.168.1.64 255.255.255.192
default-router 192.168.1.34
dns-server 68.10.16.25 68.10.16.30 68.10.9.30
lease 7 23 59
Then "reservations" are made with the exclude command
ip dhcp excluded-address 192.168.1.97
ip dhcp excluded-address 192.168.1.98
ip dhcp excluded-address 192.168.1.65
ip dhcp excluded-address 192.168.1.66
ip dhcp excluded-address 192.168.1.67
Enjoy.