Make bacon less salty
Not all bacon is equally salty. Look at nutrition labels on the bacon when you go shopping, find the least salty bacon you can, and try that. You'll be best off if you cook a small amount of your meat mixture to taste, so that if you manage to end up with too little salt, you can add some back in. If it's still too salty, then all you can really do is add other, less salty meat. I imagine a burger made from 1/4 bacon would still have tons of bacon flavor.