Actually I discovered that I can add Ruby version to Gemfile while troubleshooting the problem with .ruby-version.
If Ruby version is not specified explicitly, why not let RVM choose Ruby version like it does locally? Then it will not be necessary to maintain additional integration code.
I believe this default command prevents rvm from looking into Gemfile.
$ rvm use default
If it can be replaced with command that triggers default rvm behavior, then in presence of .ruby-version the following will be unnecessary too.
rvm use $(< .ruby-version) --install --binary --fuzzy