Passing last IP octet to a host alias and have it added to complete full proxycommand with ip address

I wish to have this all done in the ssh config file for a specific user. The site has hard-coded ip addresses into there various software and using the naming convention is not really an option.

Host bast.aws1.prod
  HostName bastion.aws1.chaos.com
  User chaos

Host *.aws1.prod
  User chaos
  Proxycommand ssh bast.aws1.prod -W 192.168.10.echo %h | cut -d. -f1:%p

Host bast.aws2.prod
  HostName bastion.aws2.chaos.com
  User chaos

Host *.aws2.prod
  User chaos
  Proxycommand ssh bast.aws2.prod -W 192.168.12.echo %h | cut -d. -f1:%p

So if I run the following command: **ssh 169.aws2.prod** it should execute within the proxy command **"ssh bast.aws2.prod -W 192.168.12.169:22"** but it executes **"ssh bast.aws2.prod -W 192.168.12.echo %h | cut -d. -f1:22"** instead. ***What is the best way to pass the last octet to the value within the proxycommand?*** Alternative ways are welcome.