layout_heights <- function (k,dl=0,ncol=1) {
    # to set up layout without 'dl' lines between plots
    # use like layout(1:5,heights=layout_heights(5))
    if (k==1) return(1)
    layout(matrix(seq_len(k*ncol),ncol=ncol))  # this changes par("csi")
    ds <- dl*par("lheight")*par("csi")
    eps=par("mai")[c(1,3)]
    dh=(par("din")[2]-sum(eps)-(k-1)*ds)/k
    return(c(eps[2]+dh+ds/2,rep(dh+ds,k-2),eps[1]+dh+ds/2)/par("din")[2])
}


# Example:
spacing <- 1
fig.rows <- 5
opar <- par(mar=c(4,4,2,1)+.1,mgp=c(2.5,0.8,0))
layout(matrix(1:fig.rows,ncol=1),heights=layout_heights(fig.rows,dl=spacing,ncol=1))
opar2 <- par(mar=c(par("mar"),spacing/2)[c(5,2,3,4)])
for (k in 1:fig.rows) {
    lastone <- (k==fig.rows)
    if (lastone) { par(mar=c(par("mar"),opar2$mar[1])[c(5,2,3,4)]) }
    plot(1, xaxt=if(lastone){"s"}else{"n"},
            xlab=if(lastone){"x"}else{""} )
    par(mar=c(par("mar"),spacing/2)[c(1,2,5,4)])
}
par(opar)