If I understand what you are after, you would like to adjust the x-axis scale so that there is more space on the left for the labels? You can achieve this using ggplot2's scale_x_continuous function.
I don't have the data clado2, but using the example code from the ggbiplot GitHub README:
library(ggbiplot)
data(wine)
wine.pca <- prcomp(wine, scale. = TRUE)
ggbiplot(wine.pca, obs.scale = 1, var.scale = 1,
groups = wine.class, ellipse = TRUE, circle = TRUE) +
scale_color_discrete(name = '') +
theme(legend.direction = 'horizontal', legend.position = 'top') +
scale_x_continuous(limits = c(-5, 5))
Hope this is helpful.