r - Remove a library from .libPaths() permanently without Rprofile.site

Question

How can I permanently remove a library in R?

.libPaths()
[1] "\\per-homedrive1.corp.riotinto.org/homedrive$/Tommy.O'Dell/R/win-library/2.15"
[2] "C:/Program Files/R/R-2.15.2/library"                                            
[3] "C:/Program Files/RStudio/R/library"     

The first item is my corporate "My Documents" folder, and the apostrophe in the path from my surname is causing all kinds of grief when using R CMD INSTALL --build on a package I'm making, not to mention issues using packages installed there when I'm offline from the network.

I want to use C:/Program Files/R/R-2.15.2/library as the default instead, but I don't want to have to rely on an Rprofile.site.

What I've tried

> .libPaths(.libPaths()[2:3])
> .libPaths()
[1] "C:/Program Files/R/R-2.15.2/library" "C:/Program Files/RStudio/R/library" 

That seems to work, but only until I restart my R session, and then I'm back to the original .libPaths() output...

Restarting R session...

> .libPaths()
[1] "\\per-homedrive1.corp.riotinto.org/homedrive$/Tommy.O'Dell/R/win-library/2.15"
[2] "C:/Program Files/R/R-2.15.2/library"                                            
[3] "C:/Program Files/RStudio/R/library" 

I thought maybe .libPaths() was using R_LIBS_USER

> Sys.getenv("R_LIBS_USER")
[1] "//per-homedrive1.corp.riotinto.org/homedrive$/Tommy.O'Dell/R/win-library/2.15"

So I've tried to unset it using Sys.unsetenv("R_LIBS_USER") but it doesn't persist between sessions.

Additional Info

If it matters, here are some environment variables that might be relevant...

> Sys.getenv("R_HOME")
[1] "C:/PROGRA~1/R/R-215~1.2"
> Sys.getenv("R_HOME")
[1] "C:/PROGRA~1/R/R-215~1.2"
> Sys.getenv("R_USER")
[1] "//per-homedrive1.corp.riotinto.org/homedrive$/Tommy.O'Dell"
> Sys.getenv("R_LIBS_USER")
[1] "//per-homedrive1.corp.riotinto.org/homedrive$/Tommy.O'Dell/R/win-library/2.15"
> Sys.getenv("R_LIBS_SITE")
[1] ""

I've tried Sys.unsetenv("R_LIBS_USER") but this also doesn't stick between sessions

Answer 1

Just set the environment variable R_LIBS in Windows to something like

R_LIBS=C:/Program Files/R/R-2.15.2/library

Restart R.