If you are on Windows. Go to the computer with wallet and open the command window and type ipconfig then look for your IPv4 Address. Make sure you use that ip address in your bat on the non wallet computer.
Example. If wallet computer ipv4 address is 192.192.1.921 your bat should look something like this: spreadminer -o
http://192.192.1.921:41667 -u USERNAME -p PASSWORD
I also use rpcport=41667 in my config file. If you change anything in your confige file you must restart the wallet.
NOTE: I am a rookie compared to tsiv but this is how I solo mine from multiple computers to the main with the wallet. I have other steps that I must do but they are not the most secure way that I have read about how I do it but it works fine for me. Been mining at time a total of 3 computers into the one with the wallet.
Running JSON RPC over internet is insecure. It allows any intermediate node to intercept your communications (including your RPC password). This is especially dangerous if you are mining on unlocked wallet because it would allow to steal your coins.
This article describes how to use secure RPC connections:
https://en.bitcoin.it/wiki/Enabling_SSL_on_original_client_daemonOf course you can instead assume that your internet provider is not interested in stealing your information as well as anyone else who has access to your traffic (NSA maybe).