If Rstudio hasn't built and cached a package, are you able to install it?

So @josh ... does this mean that if Rstudio hasn't built and cached a package you may not be able to install it? I use a miniCRAN repo hosted on github for extra control over what packages are used (see link below). Is there a way that I can build these packages for Rstudio cloud myself?


Split from topic: I can't install packaged Xgboost - #4