cannot set the path to installed R packages when building a package vignette

Dear colleagues,

I am having issues trying to build a R package I recently wrote.
I am using R 2.14.0 and my package depends on another package called aod.
Running:
R CMD Sweave vignette.Rnw
is perfectly fine and the vignette compiles properly.

but when I use
R CMD build mypackage
to build the tar.gz  I get the following error:

  * installing the package to re-build vignettes
* creating vignettes ... ERROR
Loading required package: aod
Warning in library(pkg, character.only = TRUE, logical.return = TRUE,
lib.loc = lib.loc) :
   there is no package called ?aod?

Error: processing vignette ?ExomeDepth-vignette.Rnw? failed with
diagnostics:
  chunk 1 (label = load)
Error : package ?aod? could not be loaded
Execution halted

I can fix the issue by inserting the following line into my vignette:
.libPaths(c("/ugi/home/shared/vincent/libraries/R/installed", .libPaths()))
where the path specifies the installation path to my R packages. But
clearly this should not be part of the vignette.

Basically I cannot find a good way to specify a path to my installed
packages when I run
R CMD build
I cannot find the right info. I am probably being slow but if someone could
point me to the right direction, any help would be very much appreciated.

Thank you in advance,

Vincent