I was struggling with the same issue for quite a long time, and as conan 1 is now well on its way out, I decided to take bits and pieces from cmake-conan v1 to create cmake-conanfile.
This cmake module will allow you to invoke conan multiple times from CMake, and can be configured to create a fully isolated conan environment for the project. If conan isn't installed on the system, it can also create a Python virtual environment and install the specified conan version.
If it can help you, feel free to give it a go and report any issue or feature request!