You can upload files through FTP even when your domain is under propagation.
You need to use a server IP address instead of ftp.yourdomain.com as Host Name.
Configuration when domain under propagation:
For example :
HOSTNAME: 164.132.163.21
USER ID: username
PASSWORD: your hosting password
After you log in to your FTP account make sure that you upload your html, images and scripts, etc in your public_html or www directory.