Looks like the following command does it:
wget http://www2.ati.com/drivers/linux/$(curl -s http://support.amd.com/us/gpudownload/linux/Pages/radeon_linux.aspx | sed -n 's/^.*\(ati-driver-installer^"]*\)">.*/\1/p')
I’ll add it in atiupgrade soon, so it will try this before the version hardcoded in the script.