hi in checkpoint there is no issue in sending the traffic out back of the same interface . so in checkpoint u just need to add a static route for the 10.10.x.x network pointing to the cisco router. rest everything should work fine.
if u are not good with the cli i hope u are using checkpoint splat right. open the gui of the checkpoint. i guess it should be
https://172.18.1.1.
in the gui there is a link for network connections just add a route for the 10 network and specify the gateway and the exit interface.
this should do the work.
let me know it doesn;t work out. i will surely try to help u out.
regards
sebastan