I don't have a second connection to test this on, but try anyway. Post a comment if any step fails, or if I'm doing it entirely wrong.
Configure the network to only route some packets through the dial-up connection:
Find out the dial-up connection's default gateway. It's in the Status window of the connection, in
ipconfig, and (if you know what to look for) in
1½. Find out the data logger's IP address using
Disable addition of the default gateway for your dial-up connection.
- Connection properties → Networking → TCP/IP → Properties → Advanced...
- Disable Use default gateway on remote network
When you connect, add a route to just the data logger.
route add 18.104.22.168 22.214.171.124
126.96.36.199 would be the data logger's address and
188.8.131.52 the gateway's address (which you wrote down in step 1).
If it works, and you want it to persist reboots, then add the same route again, with
route -p ... this time.