Derk, it's a highly-requested feature, but unfortunately, it's not so easy to implement.
We'll get down to it soon.
For now you can:
1. keep the sh script you want to use in the repository
2. add two actions to the pipeline:
- upload script.sh by SFTP
- execute script.sh by SSH
Then, you'll be able to use multiple lines and connect the lines with "\".
Additionally, the scripts are versioned, so you can always get back to the previous script version.