Try with design sessions upfront, i.e. discuss how the problem should be solved in terms of patterns and architecture. Once that is agreed, with 2-3 people, then the code review becomes simply a matter of style and there you can only invite for consistency with the rest of the code base. Often the problem is in the tools, face to face conversations, pair programming, human interaction help with that. You can also have your colleague help with a task of yours and show that you appreciate his input.