[geomark]

can only install packages from the interpreter

Not completely sure this is what you mean, but you can certainly run install.packages("package") right in your code, doesn't have to be done interactively. Usually want to first check if it is already installed, like with require("package").

[jrimbault]

I thing cshenton wants to install packages without running the R interpreter. Think of pip install, cpan, cargo...