Short answer: No.
The Git panel in RStudio is tied to working with projects, however, RStudio has a built-in terminal in which you can use Git, this is more advanced and less visual though. If you don't want to learn how to use Git from the command line yet, you could also open whatever .R files you want to add to a Git repository, in a project tied to this repository and use the Git panel. I would recommend you though, that when you have a good understanding of how Git repositories work, you should learn how to manipulate them using the command line.
Check these sites out for more information:
Hope this helps!