I solved a similar problem to ensure a library was installed by putting the following snippet at the start of my R code block, in this case for the sm library:
s = getOption("repos") # hard code the UK repo for CRAN
s["CRAN"] = "http://cran.uk.r-project.org"
options(repos = s)
rm(s)
install.packages("sm")
library(sm)
I think you should be able to adapt it to ensure that the relevant package is installed into the R instance which KNIME uses. I can’t remember the details as to why I needed to hardcode the UK cran repository unfortunately!
Steve