Drawing multiple vector graphics in R on one page with grImport

I'm trying to use the grImport package to draw several vector graphics on one page:

grid.newpage()
grid.picture(pic1)
grid.picture(pic2)

This just draws over the older graphic. I'm looking for something similar to par(mfrow=c(2,1)) with plots, but mfrow doesn't seem to work with grid.picture.

I know you can set x y width and height values in grid.picture, but is there a simpler way similar to par?

Thanks

require(grImport)
hourglass <- new("Picture",
                 paths= list(new("PictureFill",
                                 x=c(0, 1, 0, 1),
                                 y=c(0, 0, 1, 1))),
                 summary= new("PictureSummary",
                              numPaths=1,
                              xscale=c(0, 1),
                              yscale=c(0, 1)))

g1 <- pictureGrob(hourglass, use.gc=FALSE,  gp=gpar(fill="red"))
g2 <- pictureGrob(hourglass, use.gc=FALSE,  gp=gpar(fill="blue"))

require(gridExtra)
grid.arrange(g1,g2, ncol=2)