Determining/forcing a uniform logo symbols stack order

[mathieudupont]

With position="classic", is there a way to force the (vertical) order of the symbols, instead of using the frequency values? For example, if my symbols are "A", "C", "G" and "U" and I would like them to be always A on top of C, C on top of G and G on top of U, for each position, no matter what are their respective frequencies, how can I force that?
In the following minimal example, I would like the two stacks to be in the ACGU order.
Thank you!

library(ggplot2)
library(gglogo)

position = c(1, 1, 1, 1, 2, 2, 2, 2)
element = c("A", "C", "G", "U", "A", "C", "G", "U")
freq = c(0.27, 0.26, 0.24, 0.23, 0.26, 0.27, 0.23, 0.24)
d = data.frame(position, element, freq)

figure = ggplot(data=d) +
geom_logo(aes(x=position, y=freq, label=element, fill=element), position="classic")

pdf("minimal_example.pdf")
print(figure)
dev.off()

minimal_example.pdf