# Export your data.frame to a csv file
write.csv(YourDataFrame, file="Path/To/File.csv", row.names=FALSE)

# Read in the lines of the file
fileLinesTemp = readLines("Path/To/File.csv")
# Add a bunch of commas to add columns
fileLinesTemp = gsub(",", ",,,,,,,,,,,,,,,,,,,,,,,,", fileLinesTemp)

# Write the new lines back to the file
fileConn = file("Path/To/File.csv")
writeLines(fileLinesTemp, fileConn)
close(fileConn)