As a fellow Kelpie owner, I can feel your pain. My girl was the WORST puller and on top of that, she was dog aggressive so can you imagine we would walk past other dogs I hated walking her, and we all know if theres one thing a kelpie needs, its exercise.
I can happily say, she is a beautiful 'heeler' now
With a lose lead, hold a treat by your side where you want him to be walking. Say a clear, firm 'heel' and walk say, a metre with the treat in front of him, so thats what he's concentrating on. Stop and praise and then continue another metre.
This should be part of his training, not carried out when you are doing normal walking, so keep it to 5-10 minutes. A Kelpie/BC etc. can usually stay 100% concentrating for about 8 minutes.
In the mean time, a gentle leader, if used properly, can be quite effective, just to make it easier for you. But please do the training, as a GL isn't incredibly comfortable for the dog.